ML20010A805
| ML20010A805 | |
| Person / Time | |
|---|---|
| Issue date: | 06/27/1979 |
| From: | Ryan Alexander NRC OFFICE OF STANDARDS DEVELOPMENT |
| To: | Garcia L ENVIRONMENTAL PROTECTION AGENCY |
| Shared Package | |
| ML20010A806 | List: |
| References | |
| FOIA-81-77 NUDOCS 8108120250 | |
| Download: ML20010A805 (44) | |
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%....,.A Mr. Luis Garcia Federal Guidance Branch U.S. Errtironmental Protection Agency 4
I Washington, D. C. 20460
Dear Mr. Garcia:
The purpose of this letter is to recomend a method for calculating (1) occupational annual limits on intake (ALI's))for radionuclides, and (2; associated derived air concentrations (DAC's. We are proposing this method for inclusion in :ne new EPA guidance to Federal agencies on occupational radiation protection now under development.
A. verbal presentation on this method was presented by R. E. Alexander of the NRC staff on March 30, 1979, at a meeting of your interagency comittee on the new guidance. This letter documents the presentation made at that time.
As presently drafted, the new guidance would specify that, for a one-year intake of a given radionuclide, the average dose commitment to the three most highly irradiated organs should not exceed 5 rems.
It would also be necessary to assure that the dose to the breasts, gonads, skin and eye lens would not exceed specified annual limits. This method (1) requires
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the acceptance of a 15 rems limit for the thyroid and bone for no reason other than administrative convenience, (2) does not take advantage of generally accepted risk data that are now available, (3) does not consider the risk to organs other than the three most highly irradiated, and (4) is a complete departure from the recommendations of the ICRP 3
Publicatien 26 (ICRP-26) whereas, in our view, a partial departure could avoid shortcomings of ICRP-26 while allowing greater consistency with the methods apparently to be used in most other countries.
According to the new ICRP method, for each radionuclide the ALI is defined from the following equation:
5 REMS r
where, if the ALI is in uC1, H50T is the 50-yr accumulated dose equivalent i
to tissue r per uCi inhaled (rems /uci), and WT is the weighting factor for tissue T.
For each radionuclide and each affected organ there is a specific value of WT and H50T. The ALI is obtained by suming the WT H50T products and dividing the result into 5 rems. From the derivation of the WT factors, discussed below, it will be seen that this method considers only stachsstic effects, viz., genetic effects and cancer.
l ilo organ dose limits are necessary; for a given radionuclide the maximum dose received by any organ varies with the weighted doses received by other affected orgar.s.
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B108120250 810409 r
Mr. Luis Garcia Listed in the first column of the table below are the organs for which the ICRP has established a risk fac+or; the risk factor is shown in the second column. The ICRP's values for WT appear in the third column; these values are obtained by dividing the sum of the risk factors from the second column back into each individual risk factor, i.e., through normalization to the sum.
Tissue Risk Factor WT Gonads (genetic) 4 x 10-5 rem-1 0.25 1
Red Bone Marrow 2 x 10-5 0.12 Bone Surfaces 5 x 10-6 0.03 Lung 2 x 10-5 0.12 Thyroid 5 x 10-6 0.03 Breast 2.5 x 10-5 0.15 All Other Tissues Combined
- 5 x 10-5 0.30 TOTAL 16.5 x 10-5 1,00 Use 5 organs or tissues of the remainder receiving the highest dose equivalent.
for stochastic effects, is obtained by dividing the ALI by The OAC,9cm3, the Volume of air breathed annually by the " reference 2.4 x 10 man" during 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> at work.
Some health physicists have found this method to be attractive because consideration is given to the risk to essentially all of the irradiated organs, rather than to only the organ receiving the largest dose (the critical organ) as in the past. We strongly endorse this approach and recommend it to the EPA with certain changes as discussed below. Powever, the method presents one very serious problem which must be overcome.
Some radionuclides are deposited almost entirely in onl' one organ, and y
in the calculation of the ALI only the H50T for that organ is large enough to influence the result.
In such cases the dose comitment permitted by the ALI is 5
i ALI x
t j
The acceptable dose limits implied by this method are listed below:
Gonads 20 rems / year i
Red Bone Marrow 42 Bone Surfaces 167 i
Lung 42 Thyroid 167 Breast 33 T,
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Mr. Luis Gar cia Organ doses of 'his magnitude are clearly unacceptable.
i To solve this problem the ICRP has adoptad a rationa' 3 for~ ensuring that no organ would receive a dass so large from onu ALI.
For each radio-nuclide the ALI is calculated according to a second procedure:
ALI x
H50Tmax 50 rems This procedure makes no use of the weighting factors and employs only the largest value of H50T used in the initial method, i.e., the method based on stochastic effects as described above. This procedure is similar to the critical organ approach formerly employed by the ICRP. The value for the ALI (and DAC) is then the smallest value of the two that have been obtained.
In this manner no organ is allowed to receive a dosa comitment greater than 50 roms from one ALI, and many would receive much less.
No justification is given in ICRP-26 for the selection of the 50-rems value shown in the equation above, and this choice has been highly criticized in tne United States. We consider the selectio.1 to be unfortunate and unnecessarily high. We do not recomend it to the EPA, and we do not anticipate that its use would be accepted by our Comission.
In ICRP-26 it is indicated to be a limit for non-stochastic effects, by which is apparently meant effects that are virtually certain to occur if the dose is sufficiently large, e.g., lens opacification, acute radiation syndrome, etc.
While we endorse the general method for calculating ALI's and DAC's that the ICRP has introduced, and recomend it highly to the EPA, we are not able to accept their derivation of the weighting factors (WT) or their procedure for placing an upper limit on the organ dose commitment.
Addressing first the weighting factors, we note that the ICRP derived its WT values without giving due consideration to the genetic r) ks to persons born in' generations after the second generation, and without giving due consideration to non-fatal cancers. We believe that full consideration should be given to these risks in the derivation of radiation dose limits, cnd we have been pleased to find that such consideration has been given by the EPA staff in the development of the draft guidance to Federal agencies. The risk factors developed by the EPA staff, which include the risks omitted by the ICRP, appear to us to be reasonable and acceptable in the light of the existing literature, although we recognize that the forthcoming publication on this topic by the BEIR Comittee may result in some alterations by the EPA staff. It is our first recomendation that the IPA staff (1) derive a new set of weighting factors (W ) based on its own risk factors, and (2) calculate the ALI T
and DAC for each radionuclide of interest, using the new ICRP method for stochastic effects, the ICRP values for H50T, and the EPA values for W -
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Mr. Luis Garcia Turning now to the problem of establishing a reasonable upper limit on the organ dose, we would call to your attention the fact that the organ dose limits that have been in usa for many years in applications of the critical organ concept are, in general, based on human experience with exposure to internally deposited radium. Thus the old radiobiological basis for establishing upper organ dose limits would appear to be sound.
although the old system considers only the critical organ.
It is our second recomendation that the EPA staff calculate the ALI and DAC for The each radionuclide of interest using the critical organ approach.
organ dose limits on which present EPA (FRC) guidance is based should be employed, but the metabolic models and organ dose calculational techniques recently developed by ICRP Comittee II should be used.
It is our third recomendation that the EPA recomend as guidance to Federal agencies the smallest of the values calculated using these two approaches for each radionuclide. In this manner the ALI's and DAC's used in this country would be based on all radiation riaks to all affected organs, using the most current data and calculational techniques, and in no case would any increase in the risk to any organ be permitted.
Y trust that the EPA staff will give full censideration to these r ecommendations.
Sincerely, NG.
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Robert E. Alexander, Chief Occupational Health Standards Branch Office of Standards Development cc: EPA Interagency Advisory Comittee on Occupational Guidance to Federal Agencies l
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
% e8' WASHINGTON D.C.
20460 C
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SUBJECT:
Preference of an RPG-Based System of Dose Limitation over One Based on Risk Weighting Factors 70:
Participants, Interagency Committee on Federal Guidance for Occupational Exposures to Ionizing Radiation The two enclosed appendices - ( A) Analysis of Using Various Weighting-Factor Schemes as a Base for a System of Dose Limitation, I
and (B) Analysis of Alternative RPG-Based Systems of Dose Limitation for Occupational Exposures - are fer your study and review prior to the Cocsittee meeting to be held in Crystal Mall Building No. 2, Room 813, on Friday, May 18, 1979, from 0900 to 1600. This caterial is simultaneously being reviewed within EPA.
Please be fully prepared to discuss and to take a position en:
(a) the best base for the system of dose limitation, and (b) the preferred system of dose limitation. There are, of course, many more possibly acceptable systems than the limited number presented in the attached enclosures. You are thus encouraged to develop (in written form) your own preferred one which you would recom=end to EPA for adoption.
Also enclosed are copies of ecm=ents received to date from committee participants en their position on three basic issues: (1)
Definition of Radiation Worker; (2) The Numerical Value for the Annual Wholo-Body RPG; and (3) Limiting the occupational lifetime dose.
Those of'you who have not as yet submitted your written position en these 3 issues are reminded to please do so now.
Please let me know if you will or will not be able to attend the next and very important Co=mittee meeting. If you will not be able to cttend, I would appraciate your sending me your comments on the enclosed materials, either by mail or with your alternate attending said meeting.
(
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is c. G. cia Chairman 2 Enclosures
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APPENDIX A ANALYSIS OF USING VARIOUS RISK WEIGHTING-FACTOR SCHEMES AS THE BASE FOR A SYSTEM OF DOSE LIMITATION FOR OCCUPATIONAL EXPOSURES The Interagency Committee on Federal Guidance for Occupational Exposures to Ionizing Radiation has recommended that EPA seriously consider adoptir.g as the basis for its forthcoming recommended system of dose limitation, a weighting-factor approach similar to that in ICRP-26. The EPA veighting factors, however, could be based on both the lethal ar4 non-lethal cancer risks and the. genetic risk to all progeny generations, as opposed to the ICRP-26 weighting factors based solely on the lethal cancer risk and the geretic risk to only the first two progeny generations. The new scheme would be made subject to independent constraints such as the "non-stochastic" ones in the ICRP-26 scheme, namely, 30 rems to lens and 50 rems to all other organs.
A detailed analysis (available on request) was made of the results of using the follcwing sets of risks as the bases for the weighting fagtors:
(1) Lethal Cancer Risks (a)
(2) Lethal and Non-Lethal Cancer RMks (a,b)
(3) Lethal and Non-Lethal Cancer Risks plus Genetic Risk to all pmgeny generations (a,b,c)
These results are summarized in Table A-1.
For comparison purposes, the corresponding information for the ICRP-26 scheme is also presented in that Table. Principal results are as follows:
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(1) An (a,b) base:
(a) About doubles the a-based RPG of organs whose cancers anr nearly 100% lethal.
(b) Significantly reduces the a-bas;d RPG of organs whose cancers are primarily (e.g., 90%) non-lethal.
(c) Has effectively no impact on the a-based RPG of organs whose cancers are about 50% non-lethal.
(d) hesults in only 2 organs (breast and thyroid) having an RPG of less than 30 rems as opposed to 3 organs (breast, red bone marrow, and lung) having an a-based RPG of less than 30 rems.
(2) An (a,b,c) base:
(a) RPG's must be expressed as ranges instead of single numbers. The (a)- and (a,b)-based RPG's would also be in ranges if all 4 of the BEIR-1 models had been used. The single values expressed p
here are estimates based on the absolute risk life plateau model only.
(b) The lower (a,b,c)-based RPG's are only somewhat higher than the sa,b)-based ones. The (a,b,c)-based RPG for gonads, however, is 100 rems, as opposed to the " constraint" RPG of 5 rems.
(c) The higher (a,b,c)-based RPG's are two to three times higher than the (a,b)-based ones. The (a,b,c)-based RPG for gonads is 8 rems, as opposed to the (a,b) " constraint" RPG Of 5 rems.
(d) If an " effective" constraint RPG of 30 rems is adopted, the lower (a,b,c)-based RPG of all organs would be 30 rems, including gonads but excluding breast (24 rems) and thyroid (28 ress). Also, the higher (a,b,c)-based RPG of all cegans would be 30 rems, excluding onlygenads (8 rems).
3 f
T As indicated by the results of the above exerciss, adding the non-lethal cancer risks (b) and the genetic risks (c) to the basis for determining the weighting factors, does not wholly lead to the desired results. The problem may be said to be due to the mathematical structure of the weighting factor scheme. But this is not wholly true; the REAL probles is due to equally weighting lethal cancers, nrn-lethal cancers, and genetic effects. Until such time as all of these different end effects can be translated into commensurate units of harm, there can be no truly acceptale means for applying the weighting factor scheme on the basis of all these different end effec ts.
To attempt to bring this about is a considerably larger problem than developing a new guidance, and is certainly out of scope here.
l Additionally, there are large and varying degrees of uncertainties in the organ risk factors estimated on the basis of current knowledge on dose-effects. The lethal-cancer risk factors (Rg,) shown in Table A-1 were estimated on the basis of the i
absolute risk, life plateau model of the LEIR-1 report. We have no estimates based on the other models. Existing information indicates that for certain organs the relative-risk model may be the more appropriate ene. So, a more accurate aggregation of lethal-cancer risk factors fmm which to derive the weighting factors for a given set may have to be based on a mixture of values obtained from both the relative-and absolute-risk models. Furthermore, the risk factors for the non-lethal cancers (R
) are even more uncertain. The ones 1
3
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_. - - _ _. _ _ -....,. _,,... _ -. _.. _. _ _. _ _... _ _ _. _ _ _ _, _. _.. ~. ~.. _ _ -
e used in Table A-1 are based on assumed percentages of lethality for some of the cancers concerned -- but it appears that there are no inflexible, universally accepted values for them -- and even the concept of what is a non-lethal cancer may be subject to any number of As interpretations when it is pinned down to quantitative specifics.
if this is not enough, the genetic risk factors applicable to humans are subject to even larger uncertainties than the somatic risk factors.
It can thus be concluced that it would be intellectually dishonest to give the impression that the risk factors are known with rems to organ i is the sufficient accuracy to say that a dose of Hg
" risk-equivalent" of (W x H ) rems to whole-body. It would be g
more truthful to indicate the conditions whereby given do-es to individual organs =ay be considered the " control equivalent *of the whole-body RPG. This distinction is more than an
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academic exercise. Thus, it is concluded that at thin point in time
-- if we are to be honest with ourselves and everyone elso -- we must base the new system of occupational dose lim!tations en something other than " risk weighting factors."
Undesirable features of a system based on risk weighting factors (and constraints), other than those mentioned above, include:
l (a) The organ weighting factors are mathematically interrelated such that a change in the risk factor of any one organ necessarily changes all of the weighting factors. This is because the l
weighting factor of any one or3an is a function of the sum of all the organ risk factors.
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(b) For many organs, the inferred and unconstrained RPG's are j
numerically higher than the limiting dose (toostraint) based on non-stochastic effect considerations. Consequently, the " effective" organ RPG's are not risk-equal to each other nor to the whole-body RPG.
(c) Feature (b) also leads to effective limits for different partial-body exposures which are not risk-equal to each othet nor to the whole-body RPG. And likewise for the computed Annual Limits t f Intake.
(d) The mathematical rigidity of the system preludes use of appropriate safety factors for those specific organs whose risk factors are highly uncertain and for which the use of extra caution is indicated.
As discussed in Appendix B, an organ-RPG base leads to the development of an acceptable system of do::e limitation for occupational exposures.
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4 v
L.F.GARCIA/DRArr 4/23/79 APPENDIX B ANALYSIS OF ALTERNATIVE RPG-BASED SYSTEMS OF DOSE LIMITATION FOR OCCUPATIONAL EXPOSURES The first step in the development of an RPG-based system of dose limitation for occupational exposures is the selection of the annual RPG for whole-body. This matter has been amply treated separately and is not repeated here. In this Appendix it is assumed that the choice for the numerical value of the whole-body RPG has already been made.
For illustration purposes, this value is taken here to be 5 rems.
The system to be developed is a means to an end:
"he control of whole-and partial-body exposures in radiation-protection terms consistent with thos;; on which the whole-body RPG is based. Such exposures may involve any one single organ, any combination of organs, w
and any combination of whole-and partial-body exposures.
Additionally, the system must be applicable to either external or.
~
internal exposures as well as to any combination of both.
Following are the criteria used here for the selection of the numerical value for the RPG of each organ and which, in effect, define what an organ RPG is.
(a) The overall somatic risk (lethal and non-lethal cancers) of an organ RPG must. not be judged as exceeding that of the whole-body RPG.
(b) The genetic risk must not exceed that of the whole-body l
RPG. This is tantamount to saying the RPG for gonads must be numerically the same as the whole-body RPG.
l
2 s
(c) On the basis of preventing non-stochastic effects of an objectionable severity, the RPG of lens of eye must not exceed 5 rems and that of any other organ 30 rems _.
(d) Adjustments may be made to the numerical values of the RPG's for purposes of administrative simplification, p-ovided the above criteria are still met and that the benefits from such simplification are not outweighed by otherwise unwarranted restrictions (costs).
An acceptable system of dose limitations based on a set of organ RPG's would then be structured as follows:
(1) Specifi. ally determine the RPG for each organ according to criteria a to d above. Tabulation of information as shown in Table A-1 of Appendix A is considered essential for this and subsequent steps of this procedure.
(2) Group those organs considered to have a significant risk factor for lethal and non-lethal cancers (i.e., the stochtstic somatic effects) and. designate these as organs 1.
~
(3) Designate gonads as a constraint organ (c), with an RPG equal to that of whole-body.
(11) Designate as constraint organs (c) those specific organs (e.g., lens of eye, and skin) which have a significantly low somatic-risk factor and whose RPG is overwhelmingly based on the non-stochastic effects criterion (c) specified above.
(5) Specify how to determine the from
.icontrol-equivalent whole-body dose," (H )fany exp sure event E
e f
I
~
=
..z --
._.a:
3 involving one or more organs (1). The limitation for any H is the E
whole-body RPG. This scheme must be shown to meet the above-stated criteria a through d for any combination of organs.
(6) Specify that the limitation for any combination of.
whole-body doses (Hwb) and partial-body doses (H, H,) is:
g g, provided H, n RPG, - where RPG, refers RPG i
Hwb + HE to the constraint organ RPG's developed in steps (3) and (4). This scheme must be shown to meet the above-stated RPG criteria a through d for any combination of organs.
(7) The entire system of dose limitations must be shown to provide the necessary and sufficient criteria for. the computation of the Radioactivity Intake Factors (RIF's),
i.e.,
the EPA counterpart of the ICRP-26 Annual Limits of Intake (kLI's).
Five alternative systems of dose limitations based on the RPG criteria and structural steps specified above, are shown in Table B-1, along with that of ICRP-26 and of EPA draft of January 10, 1979, for comparison purposes. There are, of course, many possible systems These which could be developed on.the basis of the above criteria.
five, however, are considered as embracing the range of potential l
alternatives in the selection of the over-all best one for the new occupational exposure guidance.
Alternative EPAf1 is the closest one to the system contained in the EPA draft materf al of January 10, 1979 Alternative EPA #4 represents, in my opinion,.the highest RPG-based system we could prudently adopt - even though it. s still lower (by not quite a factor of 2) than the ICRP-26 system.
f
.... _ _ _ _.,., ~ _.... _ -, _, _ _, _.. _. _. _...., _ _... _..... _ _ _. _.. _ _ _ _.. _ _ _ _ _... _
4 Principal features af alternative EPA #3, which is roughly an overall factor of two lower than the ICRP-26 system, include:
(1) The RPG for breast is set at the value which it would have if based on the risk to females only. The risk factor for breast (male) is assumed to be effectively zero. The apparently ungainly value of 12-1/2 rems for this RPG actually makes for administrative simplification, as explained later.
(2) Having the same RPG of 25 rems for all the other organs (i) makes for administrative simplification (explained later).
This value, however, is based pri'narily on consideration of both the lethal and non-lethal cancer risks concerned. Specifically,(refer to Table A-1);
(a) The RPG for red bone marrow would be 29 rems if set s
on the basis of lethal cancers only (and 56 rems if set on the basis of both lethal' and non-lethal cancers).
(b) The RPG for lung would be 28 rems if set on thc basis of lethal cancers only (and 50 rems if based en both lethal and non-lethal cancers).
(c) The RPG for thyroid would be 26 rems if set on the basis of both lethal and non-lethal cancers (and 125 rems if based on lethal cancers only).
(d) The RPG for. the other organs (i) would be much higher than 25 rems if based either on lethal cancers or on both lethal and non-lethal cancers.
Thus, the RPG of 25 rems can be said to be somewhat conservative, but not overly so (in general), with respect to both lethal ana O
non-lethal cancer risks.
s/
f
_. _. _ _. _ _ -, _ _ _., _ _ -. _. _. _ _ _ _ _ _ _..-.~,. _.
5 The concept of the " control-equivalent whole-body dose," H '
E simplifies both preser 61 and application. Note that as applied in the alternative systems presented here, this concept applies only to the organs (ir). The doses to the 3 constraint organs (c) are independently subject to their RPG's.
In practice, the two principal RPG's for controlling external exposures are tnose of whole-body and skin. External exposures to breast (fe= ale) would be considered for practical purposes as if they were whole-body exposures. External d ses to gonads and to lens of eye would be controlled by their (constraint) RPG's.
The principal practical application of the RPG's of orgr,4s (i) will be in the computation of the EPA Radioactivity Intake Factors (RIF's)j the equivalent of the ICRP's ALI's.
Since the level of the EPA #3 Alternative System (See Table B-1) is about cre-!.alf of that of the ICRP-26 system, the RIF's would be expected to be generally about one-half of the ALI's.
The actual differences will not be known until computations are carried o.tt and comparisons made.
The following equations illustrate the significance and mathematical basis of the equation proposed here for determinin3 the
" control-equivalent whole-body dose," H, of an exposure event g
involving any cowination of doses, H, to one or more organs (1).
g Let D represer.t the highest RPG for organs (1). Then, m x RPGg=D (a) where m is a whole integer. The basic limitation is then that Hi
$, ~R P G ; - I M
A r'
l
6 is a whole number equal to one or g = D/f, where fg Since RPG f
higher; then equation (b) can be expressed as
(,t )
a But, from equation (a), D = m x RPG,g.
Thus, equation (c) becomes j
j We In equation (d), m is' an integer (i.e., a constant) determined by equation (a). The su=mation of the (f H ) for an exposure event, 1g however, may involve a number of organs (1) which is either lera than, or larger than, m.
In the RPG-based schemes proposed here, this cu=mation is stipulated to be over the "m" maximum-dosed (i.e.,
maximum-valued (f H )) organs (1) in'rolved in the exposure event.
1g The resultant su==ation, regardless of whether it involves less than m organs (1), must be divided by m.
With this understood, the
" control-equivalent whole-body dose," H, and its. limitation are:
g I H b RPG (e)
HE*
ig Because constraint organs (c) may also be involved in a multi-organ exposure event, the general limitation for a malti-organ exposure event is equation (e), subject to the condition that H,I RPG.
~
The appmpriate limitation for any combination of whole-and partial-body exposures is simply:
f
\\
e.
f l
l l
WB + H S RPG
(#}
H g
WB provided that H
- RPG, e
whers H is as defined in equation (e).
E There now remains to assure that the dose limitations specified for multiple-organ exposures (equation e) and for any combination of whole-and partial./ ody exposures (equation f) fully meet the above J
specified criteria.
According to the multiple-organ limitation (equation e),
+ 'm,% MG (I) g =k(f H33+fH22*
H H
WB or s2 (2) f!,
R,
+... +
l
)
(m)RPGWB/fm (m)RPGWB/f2
/
(m)RPGWB/f1 i = RPG, the above expression is and, since (m) RPGWB'I 1
equivalent to H /RPg+H /RPG2 +... + F /RPG,6 1 (i) 3 2
From this, it can be seen that the maximum dose permitted to any one of the " maxi =um-dosed" m organs is its RPG. And since the
"=aximua-dosed" m organs are actually those with the maximum-valued H /RPG, for any of the dosed organs (1) excluded from the l
1 y
H /RPG i 1 and H b RPG.
equation for HE g
g g
The maximum uniform dose, H, permitted to any aggregation of k (bm) organs (1) is that for which - per equation (g),
- d-S.hf;=.RPGws i
on RPGs q)
R = w+-
A.-
f
O g=1,thenI,f m, and H = RPG If any If each f g
g.
4 s greater than unity, as in Alternatives EPA #3 and one of the f i
EPA #5 (where it is 2 for breast-female), then (1/m)f fg1 and H 4 RPG g.
This is a " flaw" in an RPG-based system in which all of the organs (i) do NOT have the same RPG. It could be serious enough to preclude the adoption of alternatives such as EPA #3 and EPA #5 -
which promised use of the g factor as an independent means for making changas to the individual organ RPG's (as may be required later) without perturbing the whole system. Let's investigate this matter further.
In Alternative EPA #3, ft = 1 for all organs except breast (female) for wnich it is equal to 2'.
In this system, the value of H would be j=d
.a,
when breast (female) is one of the or gans involved in the summation.
Hence, in this system the value of H would be H = (5/6) RPG g j i.e.,
ene-sixth smaller than the one that theoretically should be permitted. Some may consider this to be an unacceptable situation.
Sikilarly for Alternative EPA #5, the value of H would be H = (6/7) RPG,g.
In similar alternative syst. ems containing more than one RPG with an f > 1, the resultant [f would be larger y
t 1
and hence (per equation j) the value of H would be correspondingly smaller. This situation renders the syster.: internally inconsistent, to the extent that it restricts the uniform dose to a very limited I
number of organs, to a value lower than that permitted to all organs
. ~, -
(
~
~
2.
=.
9 by the (basic) whole-body RPG. In theory, this makes the f-system, in general, an unacceptable one - or if used, it must be done with caution, keeping in mind its inherent flaw. There is internal consistency, however, in systems making use of the provision that H
1 H
(k)
Em g
where RPG1 = constant = m x RPGg - in terms of permitting a or more organs (1) to receive a uniform dose equal to RPGg.
In such a system, however, care must be takan in the choice of the value of RPG. This is due to the fact that equation (k) is in 1
essence equally weighting the dose of each organ 1, the " inferred" weighting factor being (1/m). As seen from entries in Table A-1 of Apoendix A, the estimated risk-based weighting factors do vary considerably from one organ to another. The choice for RPG
^
g therefore must be made in such a manner that:
(1) It provides a level of ptatsetion to the most radiosensitive From estimates crgans (1) which is fully consistent wit h the RPGg.
in Table A-1 of Appendix A, the value of a should 'b6 no higher than 5, based on breast-general, rather than breast-female.
The corresponding value; of RPG1 (for RPGg = 5) is thua 25 (2) It is no higher than, nor unreasonably lower than the limit adopted on the basis of the sortatic non-stochastic effects - namely, 30 rems proposed here. This is in censideration of the fact.that the risk factor of many of the organs concerned are estimated as
)
significantly it.wer than those of the three or four most 1
radiosensitive ones (namely, breast, red bone marrow, lung, and possibly thyroid).
l i
\\
f
-c------,
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,,--e-,w
10 v
Thus, on the basis of current risk estimates, it would appear 1 = 25 rems affords a level of protection to the 3 (or 4) that an RPG most radiosensitive organs which is comparable to the RPG.g of 5 Also, it is not unreasonably lower than the 30 rem's rems.
non-stochastic limit. This argues for selection of Alternative. EPA In spite of the above-discussed flaw in an f-system, Alternative
- 2.
The theoretical flaw
- 3 may actually be the better choice of the two.
from having f = 2 (i.e., an RPG 12-1/2) for breast (female) will very likely 61ve rise to no serious problems in practice.
The RPG-based system discussed here does not really do sway with all of the undesirable features inherent in a risk weighting-factor system such as that of ICRP-26. The RPG-based system, however, does i
appear to be simpler and more flexible and conservative - and it is also more consistent with the facts as known.
j RECOMMENDATIONS It is not surprising that there are some inherently objectiontble I
(but hopefully tolerable) features in a system grossly simplifying, for practical purposes, a highly complex matter involving a nucher of interrelationships. Consequently, in spite of the bad features which have thus far been uncovered, it does appear to me that at the current time an RPG-based system is preferable to one based on a set of risk I
I thus recommend Alternative System EPA #2 (or weighting factors.
- 3), shown in Table B-1, as the one to adopt for the new occupational exposure guidance.
5D
.. a
==.
i 11 COMPARISON OF THE EPA #3 AND ICRP-26 SYSTEMS The essential, differences and sim41arities between Alternative System EPA #3 and that of ICRP-26 are:
1.
The whole-body RPG of both is the same.
2.
ICRP-26 includes gonads in the computation of t.%e
" equivalent" whole-body dose; EPA #3 does not. The EPA system limits the dose to gonads to 5 rems; the ICRP limit is' 20 rems.
3 The EPA #3 system limits the dose to breast (female) to 12-1/2 rems, e.d to any other organ (i) to 25 rems. The ICRP-26 limits for those organs are:
B rea st---------------33 Reo Bone Marrow----------42 Lung ---------------------- 4 2 Any other organ (1) - ------50 Both ' he ICRP-26 and EPA #3 systems treat lens of eye and 4.
t skin as " constraint" organs. The RPG's, however, are different:
EPA #3 ICRP-26 Lens of Eye 5 rems 30 rems Skin 30 rems 50 rems 5.
For multiple-organ exposures, the limitations in the two systems are:
$g provided that H d RPG, where (f H )e refers to the 5 maximum e
gg x
{
e
12 a 1 for all orsens (f H ).in a given exposure event, and f gg g
except breast (female) 'for which f : 2.
(In EPA #2, all fg: 1, and thus HE = (1/5)
H.)
g dit ICRP-26:
NH 6 5 rems HE*
i1 provided H does not exceed 30 rems for lens of ey,, and 50 rems for g
all other organs; and the values of W are those specified.
g 6.
EPA #3 vs ICRP-26:
The maximum uniform dose to 5 or more organs would be limited by EPA #3 to 5 rems if breast is not one of the " maximum-dosed" organs and to (5/6) 5 rems (= 4 1/6 rems) if treast-female is involved in the computation. The uniform dose permitted by ICRP-26 to n organs is H, = (1/I W ) 5 rems. All of the 5' organa specifically assigned a 1
value of W anc at least 5 of the " remainder" organs would have to be involved in the exposure event for W to be equal to unity and, g
hen'ce, for H to be 5 rems. In all cases involving less than those 10 r*gans, the W is less than unity; and thus H would be larger 1
than 5 rems.
The above co=parison demonstrates the basically more conservative nature of the EPA 23 system in interpreting the radiation-protection significance of a =ultiple-organ exposure event. In an exposure event involving more than one organ (1), the EPA system never permits the dose of any one of those organs to reach its RPG. An RPG not only g
limits the dose to any one organ (1); but, if any such. organ (i) receives a dose equal to RPG, the EPA #3 system precludes the 1
O i
7 e
v,------+ow r-,
-,---s---,-s
~w~m----n--,-,--,,ww
-,-v-,e
~~--e~,w--
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e
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d 13 exposure of any other organ (1), whatsoever. This feature may perhaps J
be considered as the mo'st objectionable one by those favoring adoption l
I of ICRP-26.
i The same feature would be true of the ICRP-26 system if one considered the RPG to be equal to (1/W ).5 rems. But the ICRP 1
1 does NOT permit such a dose if it exceeds 30 rems to lens of eye, or 50 rems to any other organ. The ICRP system thus consists of two types of " inferred" RPG's - (1) those which are numerically lower than the constraint (applicable only to breast, red bone marrow, and lung);
and (2) those which are numerically larger than the constraint (applicable to all but the above 3 ersans). The " effective RPG" for the three organs subject to the first type inferred RPG is (1/W ) 5 1
m as, for lens of eye 30 rems, and for all other organs 50 rems.
Delivery of a dose equal to an " effective RPG" to any one of the first-typ3-RPG organs is considered risk-equivalent to a whole-body dose of 5 rems; and hence exposure of any other cesan (except skin and lens of eye) would be prohibited. On the other hand, an " effective RPG" dose to any one of the other organs prevents further exposure of that organ, but does NOT prevent exposures of other organs. The extent to which the other organs may be exposed is determined by the basicequation[WH 6 5 rems (subject to the constraints). This 1
sophisticated, and intellectually arpealing, feature of the ICRP system, however, cannot be applied when the ALI's are being determined (such determinations being, after all, the essential purpose of the weigh,ing factor echeme). The reason is simple: the " constraint dose
.3 r-*
.~
. = -..
14 limit" to any organ will determine the ALI. No additional intake could be allowed as it would lead to further (prohioited) exposure of that limiting organ.
7.
Bottom-Line Differences The difference between the EPA #3 system and that of ICRP-26 is more than structural. It is of interest here to point out the numerical differences in the elements or principal practical significance: (1) Whole-body RPG; (2) Skin RPG; and (3) RIF's (cr ALI's).
(a) The whole-body RPG is the same in both systems, namely, 5 rems.
(b) The skin RPG in the EPA #3 system is 30 rems.
(It could be reduced to 25 rems if the benefits can be shown to exceed the costs). It is 50 rems in ICRP-26.
{c) Since the ALI's and the RIF's are not currently e
available, no direct comparisons are possible. Inferences, however, can be drawn from the structural and numeri, cal differences between the two systems. Because the organ RPG's of the EPA #3 system are rorghly one-half of the corresponding " effective RPG's" of ICRP-26, the RIF's would be expected to be about one-half as large as the ALI's.
The "effectrie" higher weighting (..' many of the organs by the EPA #3 system may possibly lead to the RIF's being even lower. The EPA system, however, involves only the 5 " maximum-dosed" organs, as opposed to the ICRP-26 involving as =any as 10 organs. For this reason, the practical significance of the diffrerences in " effective" f
15
~
weighting may be more potential than real. In other words, it appears Very likely that the values of the RIF's will, in gereral, not be much smaller than ont.-half of the corresponding ALI's.
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4
i v-t MEMORANDUM DEPARWENT OF HEALTH, EDUCATION, AND WELFARE i
rust:c HEALTN sEhVICE l
roon AND onuo AournistaATION l
Luis F. Garcia, Office of Radiation Programs DATx:
January 31,1980.
To Environmental Protection Agency i
t i
Chairman, Interagency Committee on Federal Guidance for 4
Occupational Exposures to Radiation n*
Assistant Director for Scientific Affairs (HFX-4)
FROM :
i Bureau of Radiological Health, FDA SU81ECL Consents on Draft - January 22, 1980 Federal Radiation Protection for Occupational Exposures Following are my comments and those of Mr. Gail Schmidt on the subject 4
draft. These are in no way to be construed as an official HEW response since time was not sufficient to obtain such a response, nor was it requested.
I.
1.
Page 7.
Risks from Occupational Exposure.
The first sentence should be deleted (or revised) as it implies that the three kinds of risks descrioed have, in fact, occurred l
(and been observed) due to occupational exposures. Might reviss to indicate that these types of risks are of concern.
4 l
Further, particularly on page 8, it needs to be clarified that these estimates are based on the assumed validity of the linear non-threshold theory. The average reader could not possibly follow the hidden logic on this page. Risk estimates jump from lifetime risk when evaluating the limit to annual risk when evaluating the l
average radiation worker's risk. Material ts generally presented i
with a lack of precision. For example, it is concluded that '.here is no safe level of radiation expesure because " cancer reduced at one dose is equally as debilitating a's that same type of cancer i
induced at another dose." Not so--this conclusion is based on the t
validity of the linear non-threshold theory, not or the above statement. Another example, non-stochastic effects (eye and temporary sterility), assume that severity is proportional to dose.
They are also considered to be threshold-related. The effects j
described either occur or they do not. The degree of severity.
r i
varies with dose, not the probability of occurrence. To indicate that they would not occur at the present limit "to a degree suf-ficient to be clinically detectable" is to attribute a stochastic l
(i.e., probability of occurrence) relationship and is incorrect for l
the risks described.
i 1
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GU 2.
t.ouis F. Garcia, Chairman Interagency Comittee on Federal Guidance for Occupational Exposures to Radiation The material on page 8 " leads" the reader to conclude that the present limit is associated with a high risk, but the average Since the average worker's risk is low, worker's risk is very low.
I would conclude that present practice is satisfactory.
l In addition to citing worse case for the limit, the risk estimates The are presented in an absolute rather than comparative manner.
normal risk of dying from lifetime cancer is 16 in 100. Hence, even at exposure every year at the limit, the risk is 19 to E2 in 100. Looks fairer than the way it is presently stated.
2.
Page 9.
Limitation of Whole Body (to 100 Rem)_.
The first two sentences again appear to be mixing averas doses versus limit doses and estimated bioeffects for comparison to actual deaths in other occupations. This does not keep the issue in perspective. The preamble should clarify how emergency doses are handled re the 100 rem adtronition, i.e., is it the intent of Item 4, p' age 22, that emergency doses are not considered re con-C formance to either the annual or lifetime values?
3.
Page 10. First itew Paragraph.
This motherhood statement cannot be defended at any exposure level.
If we accept the linesr non-threshold theory, then the importance of avoiding unnecessery doses also goes to zero as the dose goes to Thus, when doses become only some small fraction of back-zero.
ground, the concern alco disappears.
If not, then we are committed to an infinte task to eliminate a diminishing hazard. That is not the procer expenditure of public funds.
4.
Page 11. Middle of Page.
The basis and rationale for use of a weighted risk (ICRP-26), plus dose limit approach is not clear nor justified. Dose limits for critical organs can always be set lower to provide greater pro-tection. Why not? As stated, the basis for limits is " greater i
protection" which then leads to a zero dose limit, or at least j
lower arbitrary dose limits than those of ICRF-26. Thus, i t.
must either fully accept an attempt at a scien-i appean that we tific approach or forget it.
If the scientifically derived limits are higher than necessary, then ic:'s adopt arbitrary " safety factors" or "ALARA factors" 'or implementation. Then it would be i
! (/ o i
clear what is the meaning of the limits.
l 1
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3.
Louis F. Garcia, Chaiman Interagency c mittee on Federal Guidance for o
Occupationai Exposures to Radiation 5.
Page 11. Third Paragraph, last Sentence.
Neglects absorption through skin and by wound contamination--needs to be inserted.
6.
Page 12. First Paragraph.
Rationale for keeping 30 rem limit is arbitrary and without scien-Let's set the limit based on science and then apply tific support.
"ALARA or safety factors" (see page 11, middle of page above).
7.
Page 13. Limitation of Risk to Unborn (Embryo and Fetusj,.
Although the purpose is to protect embryo and fetus, the statement ends by protecting fertile women. Gives fertile but not pregnant women choice of working under 0.5 rem or 1.5 rem radiation limit.
Since gonadas exposure could also a.~fect a fetus (genetically),
same reasoning of choice of limit should logically be extended to males, or as an alternative, the limits should be stated for the
, y fetus.
8.
Page 14. Statement.
"The maximum annual dose for the skin of the whole body is main-tained at 30 rems, since a need for allowing higher doses has not been demonstrated" implies that if such need is demonstrated., the limit would be raised.
I l
9.
Plae 15. Bottom.
Did you mean Recommendation 8--not 7?
i
- 10. Page 16. Radiation Protection Guidance.
I Stated simultaneously in tems of dose equivalent and comitted dose equivalent is more restrir.tive to long-lived radionuclides ean short-lived ones.
(If dose rate is coniidered, perhaps it
.rould be the other way around.) Choose one. I prefer committed dose equivalent with explanation as to instantaneous comitment of dose equivalent for external exposure and probability of commitment of dose eGJivalent in first year after ingestion or inhalation for N
internally deposited short-lived radionuclides.
y-
t i
\\
j Louis F. Garcia, Chairman 4.
i Interagency Comittee on Federal Guidance for t
Occupational Exposures to Radiation
't
- 11. Page 17. Equation If Hj, in terms of annual comitted dose equivalent, then H must w
be the sum of the annual weighted committed dose equivalents.
- 12. Page 17. Recommendation 3b.
I feel that clarity would be increased if the limit for other organs is stated as 0.08 with a footnote to limit to five organs rather than giving the sum 0.40 for the five organs. H should be w
a comitted dose equivalent.
- 13. Page 17. Recommendation 3c.
Does this sum include partial body exposures (as covered in 3b) or only internal plus whole body? It should be: Hwb + H = 5 rem w
where Ha is the comitted dose equivalent from partial body and internal.
t
- 14. Page 18. Range A, b. and Range B, d.
Second statement together with first implies no professional radiation protection supervision required in Range A.
I propose that HP supervision in all ranges has helped keep average worker's
.l exposure low. Document would remove this constraint.
- 15. Page 19. Reco:mendatio Q.
This requirement is too demanding, both in red-tape paperwork and requiring an HP full time in each exposure (work situatien) that leads to the 1.5-3 rem / year doses. The intent-is to lower doses--
l not require an extra person in the radiation field.
f I
- 16. Page 19. Recommendation '3e.
l l
If annual recordkeeping is required, one should also require a lifetime record for both Ranges B and C since most workers will be in Range B, but in some years, in Range C.
As proposed, is a reduction ir, proteccion activity.
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J Louis F. Garcia, Chairman 5
Interagency Comittee on Federal Guidance for Occupational Exposures to Radiation
- 17. Pages 18-19.
The instructions / education required should increase in Ranges B and 1
i C over that for Range A.
Guide does not so indicate.
- 18. Page 19. Recomendation 4.
Last sentence: I totally do not understand what is intended.
- 19. Page 20. Recomendation 5.
The RIF should be for internal exposures, including skin absorption and wound contaminacion--not just inhalation and ingestion, which are the prcper terms, not breathing and swallowing. The RIFs-cannot meet both 3a and 3b at the same time unless one has an infinite number of values for the RIF for a given radionuclide. Be specific in the last sentence, as it.is not evident what Minimum O
Radiation Protection Requirements are.
- 20. P_a,qe 20. Recomendation 7.
See coment on page 13.
- 21. Page 20. Recommendation 6_.
Either specify or delete the reference to additional restrictions in federal law. Isn't this suppcsed to be followed by all federal agencies and law (regulations)?
l
- 22. Page 20. Recommendation'8_.
The last sentence should be deleted as this is more red-tape and r
impossible.
Indiv W al exposures may exceed the RPGs as a practi-cal matter. Further, it is not necessary to have a public record in such instances. If the intent is with regard to establishing a regulatory limit, 0.K.
That is not clear.
- 23. Page 21. Note 2 Do you mean Recomendation 3c?
3 I
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1 O
Louis F. Garcia. Chairman 6.
Interagency Comittee on Federal Guidance for Occupational Exposures to Radiation
- 24. Page 22. Note 4.
t For further clarification, add: "and are not to be counced in the lifetime dose record." Note 5 further raises the distinction between overexposures and emergency exposures. Some clarifying definitions are in order.
- 25. Page 23. Top.
There already is an effective federal program for worker radiation protection. Therefore, delete this last phrase.
Bernard Shleien, Pharm.D.
cc:
Mr. Villforth (HFX-1)
Dr. Johnson (HFX-4)
Mr. Terpilak (HFX-460)
S i
O p-*
l
m
.. a i
e Department of Energy Washington, D.C. 20545 February 1,1980 3
i I
Louis Garcia U.S. Environmental Protection Agency
(
Review of DraftiFederal Guidance for Occupational Exposures to Ionizing 5
Radiation General Statement The DOE representative is pleased with the progress made in the development of the concepts prt: anted in the draft Federal We support the major elements of the guidance, guidance, subject as above.
including:
graded set of radiation protection requiremer.ts; a
a RPG of 5 rem of the 5(N-18) per year for the whole body, including the deletion
?
4 allowance on the 3 rem / quarter limit;
~i..
the limitation of dose based on the addition of external and internal
[
radiation using the equivalent risk concept; and, bVb.
dose to the embryo and fetus be limited to 1/10 of the RPG.
However, there are several coments and suggestions generally presented it herein, which are offered for your consideration at this time. These
- }
will be discussed in detail at Friday's meeting.
the draft must be formally transmitted to the parcicipating Federal r,
agencies as a next step; e
i
- i although the Range A is useful and acceptable, combining Pange B and C should provide a greater degree of radiation protection and control t
consistent with current practices. The draft suggestions of separate
[i practices for Ranges B and C will decraase the mandated radiation protection controls for those workers between.5 and 1.5 rem; t
A i
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7
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-e
2 the RPG for the hands must be stated as applying to the total tissue of i
the hands andmot just the skin; the statement on page 12 regarding "no need for a higher value" cannot be made without the publiuticq or reference to adequately support this statement, i.e., the RIF's. It woula appear that 30 rem would not provide any serious implementation difficulty to DOE; the method of deriving the "W " appears inconsistent with the concept g
l of equivalent risk; the absolute prohibition of women of childbearing age to receive doses in excess of 1.5 rem should be eliminated. This is unnecessarily restrictive; the guidance should include an admonition that every reasonable effort should be made to limit lifetime doses to 100 rem. The guidance should not absolutely restrict lifetime doses to 100 rem; and, other clarifying type coments as will be di uss
/
r t
Edward. Y lla '
DOE M erInte[agencyTaskForce Q:c:
W. Burr, EV-30 T. McCraw, EV-30 C. Meinhold J. Selby, Battelle A. Desrosieis M. Dix, EV-12 f'
~ & y).Y,))Glh641l-/-).h c
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h
'l UNITED STATES ENVIRONMEf 4TAL PROTECTION AGENCY z,'r$J WASHlflCTCN D.C.
20460 s % peo Mc JAN 22 500
SUBJECT:
Meeting.of Friday, January 25, 1980 TO:
Participants, Interagency Cc==ittee on Federal Guidance for Occupatienal Exposures to Ionizing Radiatica The next meetin5 will be en Friday, January 25, 1980, frem 1:D0 p.m. to 4:30 p.m., in Roo.n 1119, Crystal E:til Euilding Number 2.
Plcase review the enciesed draft (1/22/20) Fedaral Remister
. notice, paying pa.rticular attentien to material undce the headin6 "Propcsed Recc=endatiens" cn pagea 16 thrauch 23 We will focus en that caterial, with the objective of resolvins any substantive controversies, and secondly, of agreeing on wording changes to clarify the intent.
We wul not discuss at the meeting tatorial under the heading U "Public Hearings. You are asked, heuever, to co=ent en the balance of the draft and to provide us with a copy of your ec=ents at the meeting.
If you will not attend, please submit your written cc :ents to me so that we have them en hand at that time.
The draft (January 10, 1979) techniesl support docu=ent is being revised, and we will send you a copy en ce before February 5, 1980, for your review. This will be acco:panied by the latest draft Federal Register notice.
We appreciate your contributions to this prograc, and helpins us to,expedito it.
Also enclosed is a current list of the Interagency Co=uittee participants.
e
, yn uis F. Garcia Chairman 2 Enclosures OG f
i e
~ - -
l Details of these and other risk estimates ws
)
iting radiation dose.
l background document..
3 use are provided in the accc panying technica d under A worker who received the largest lifeti:e dose allowe
'd retirement at age present guides (5 re=s per year fees age 18 to assume oo of 65, or 235 ress) would have a lifetize risk of about 3 to 6 in t ble chances dying from radiatien-induced cancer, and nu=erically compara/
4 in his both of non-fatal cancer and of serie:S hereditary ffrects However, in our recent national survey of exposures for halfof,andonhy descendants.'
of all workers received less than the year 1975. 99%
Based on these and other data, 0.1% exceeded, an annual dose of 5 ress.
ts have received we believe that only a few workers involved in ceciden close to the =aximum allcwed lifeti=e dese.
ll risk
'Ihe average worker exposed to radiation sustains only a sma The esti=ated average risk of death due to of de'ath frec radiation.
the risk of radiation-induced cancer is s= aller, fer example, than tional job-related accidental death in the safest of 411 =ajer occupa 60 per million categories, retail trades, fer which the death rate was We estimate that the co11Fetive dose to the =cre t work.?s,in 1975 their workplace one million workers potentially exposed to radiatica in
~
cer for that same year will not lead to =cre than 15-36 prematurc can f an Other ways of expressing this risk are that the exposure o i
lifeshortening deaths.
average worker to radiation in 1975 represented an average I
i d
f
'Esticated ranges of risk for cancer death are based on absolute an 8
ontinue to l
relative risk :odels and the assu=; tion that most cancers c Serious hereditary occur over the lifeti e of exposed persons.cffects here =ean in their 1972 I
I l
ic report as scricus dicabilitics. leading to pre =aturo death, hecophell i
fibrosis, diabetes, schi:c;hrenia, and epilepsy.
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5 rems Whole body
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5 rems Gonads
~
Lens of cy 5 rems Hands only 50 rems 30 rems Any other organ J
b.
Non-uniform exposure of the body and its organs l
shall also satisfy the condition on the sum of annual weighted dose equivalents, H,,
that
?
H, s )(,w H y 5 recs, g
L is the annual where w is a weighting factor, Hg g
committed dose equivalent to organ i, and the sum excludes the g nads.nd lens of eye. Reccmmended values of v are:
g
-0.20 Breast 0.16 Lung 0.15 Red Bene Marrew 0.04 Thyroid 0.04 Bone Surfaces 0.01 Skin O.40 Other Organs' In cases where both external and internal sources c.
of dose are involved, the sum of the annual external M*"*"
whole body dose equivalent and the annual weighted dose 1 v ~~O I p[,. sesi equivalents from radioactive Laterials in the body j
7^[a"/
shall not exceed 5 rems.
' Applies only to the 5 other cegans with highest doses enly, each being given a weighting factor of 0.03.
3
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is the external whole bcdy dose equivalent, RPG wb
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5 internal dose, and RIF) is as defined in Rece==endat en
/
i te The =etabolic odels specified by the ICRP are appropr a 3
We will recc==end other models when to use to calculate the RIF's.
they are appropriate and neccessary.
idance.
E=ergency exposures are outside the scope of this gu 4..
The Overexposures are not addressed by this guidance.
ibility of users and
~
5 equitable handling of such cases is the respons the Federal ag?ncy having regulatory jurisdiction.
~
ided by RPG's for perieds other than ene year are not prov s
6.
Limits for cther periods =sy te derived by these recc==end:tions.
d RIF's when, the Federal asencies rec = tha annual RPG's an Such li=its should be derived with recognitien of the necessary.
for Mini =u: Radiation three levels established in Reco==endatirn 3 llective doses Protection Require =ents, and with care to =aintain co as icw as is reasonably achievable.
I 1
for The above recc==endations would provide general guidance I
i It is expected that each Federal i
radiation protecticn of workers.
f crecific worker exposure j
cacncy, by virtue of its i==cciate knculedge o l!n 22 r. - - -
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