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ED04 – Skin Dose from Dermal Contamination 

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Date: April 30, 2021 

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DEFENSE THREAT REDUCTION AGENCY

NUCLEAR TEST PERSONNEL REVIEW PROGRAM

RADIATION DOSE ASSESSMENT

STANDARD METHOD

ED04 – Skin Dose from Dermal Contamination

Revision 2.0 

Cleared for Release 

Key to SOP ID Codes 

RA (Radiation Assessment - SOP) 

ED (External Dose - Standard Methods) 

ID (Internal Dose - Standard Methods) 

UA (Uncertainty Analysis - Standard Methods)
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Revision Control

Revision Revision Description Revision 

Date

Authorization 

Official

1.0 Original 10/31/2007 Paul K. Blake

1.2

- No Rev. 1.1 of this SM was produced.

- New version. Revision 1.0 (considered a working draft) was 

completely rewritten to produce Rev. 1.2. 

10/31/2008 Paul K. Blake

1.3 -Added references

-Minor editorial changes 01/31/2010 Paul K. Blake

2.0 - In Section 5.2, added SDMF values for several additional skin sites

- In Section 5.2, updated the SDMF values for consistency with 

Apostoaei and Kocher (2010)

- In Section 5.3.2, updated the values and list of skin sites for the 

Interception and Retention Fraction (R).

- Section 5.3.1, revised definition and equation for FR(t) to be 

consistent with SM ID01

- Updated reference list

- Other editorial changes

04/30/2021 James D. Franks
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Table of Contents

Table of Contents............................................................................................................................ 3

List of Figures................................................................................................................................. 4

List of Tables .................................................................................................................................. 4

1. Purpose/Summary............................................................................................................... 5

2. Scope................................................................................................................................... 5

3. Responsibilities................................................................................................................... 5

4. Definitions........................................................................................................................... 5

5. Method Description ............................................................................................................ 6

5.1 General Approach for Skin Contamination ............................................................ 7

5.2 Skin Dose Conversion Factor ................................................................................. 7

5.3 Skin Dose from Descending Fallout....................................................................... 9

5.3.1 Surface Activity Concentration – Csurf(t).................................................. 10

5.3.2 Effective Interception and Retention Fraction – Fdes................................ 10

5.3.3 Skin Dose Calculations for Descending Fallout ....................................... 15

5.4 Skin Dose from Resuspended Fallout................................................................... 16

5.4.1 Airborne Activity Concentration Cair(t).................................................... 16

5.4.2 Effective Retention Fraction – Fres ........................................................... 18

5.4.3 Skin Dose Calculations for Resuspended Fallout..................................... 19

5.5 Skin Dose Calculations from Prior Detonations................................................... 21

6. Data and Input................................................................................................................... 23

7. Referenced SOPs and Standard Methods from this Manual............................................. 23

8. References......................................................................................................................... 23
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List of Figures

Figure 1. Fall Times of Particles of Different Sizes from Various Altitudes.............................. 13

List of Tables

Table 1. Skin Dose Conversion Factor DCFskin(x,t) (rad h−1 Ci−1 m2)........................................... 8

Table 2. Recommended Values for SDMF.................................................................................... 9

Table 3. Interception and Retention Fraction (R) ........................................................................ 12

Table 4. Summary of Factors in the Calculation of Fdes.............................................................. 16

Table 5. Summary of Factors in the Calculation of Fres .............................................................. 20
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Standard Method

ED04 – Skin Dose from Dermal Contamination

1. Purpose/Summary

Standard Method (SM) ED04, Skin Dose from Dermal Contamination, provides general 

technical methods for assessing dose from radioactive contaminants deposited on skin or

clothing of individuals in the Nuclear Test Personnel Review (NTPR) Program according 

to the procedures specified in SOP RA01.

2. Scope

This standard method provides technical guidance for reconstructing skin doses due to 

beta and gamma radiation emitted from contaminants deposited on the skin or clothing. 

This standard method should not be used to determine skin doses due to alpha radiation 

or internally deposited radionuclides, nor should it be used as the sole method for 

determining skin exposures when the methods of SM ED03 - Skin Dose from External 

Sources also apply. This standard method is used in conjunction with other standard 

methods for assessing whole body radiation exposures in accordance with the 

requirements of Title 32, Code of Federal Regulations, Part 218, “Guidance for the 

Determination and Reporting of Nuclear Radiation Dose for DoD Participants in the 

Atmospheric Nuclear Test Program” (DoD, 2020).

3. Responsibilities 

Qualified radiation dose analysis staff members use these methods and associated tools 

for assessing the radiation doses for exposed individuals. It is the responsibility of the 

analysts to understand and correctly apply the methods and techniques presented below.

If situations arise where these methods and techniques are inadequate to address a 

specific exposure scenario, it is the responsibility of the analyst encountering this 

deficiency to bring it to the attention of appropriate staff personnel so that the 

methodology can be extended as required to provide adequate estimates of skin doses 

from dermal contamination. It is the responsibility of the staff member executing and 

implementing this extension to document such in a revision to this standard method.

4. Definitions

Activity concentration or activity density: 

− On a surface Radioactivity per unit surface area (typically in units of curies 

per meter squared, abbreviated as Ci m−2).

− In air Radioactivity per unit volume of air (typically in units of 

Ci m−3).
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Dermal Contamination Radioactive material deposited on the skin.

Individual Any person (member of the Armed Forces or civilian) who 

participated in the nuclear weapons testing program.

Mixed Fission Products The aggregate of radioactive nuclei that results from the 

fissioning of fissile material (e.g., U-235 and Pu-239) in a 

nuclear detonation.

NTS Nevada Test Site.

Particle Size Distribution The distribution of sizes in a collection of particles, such as 

those which comprise fallout deposited at a specific range from 

and time after a nuclear detonation. Such particles are 

classified as follows (Apostoaei and Kocher, 2010):

− Small particles Collection of particles with diameters less than 

100 micrometers (μm) and median diameter less than 50 μm.

− Large particles Collection of particles with a large fraction of particle 

diameters greater than 50 μm and median diameter 100 μm or 

greater.

− Intermediate particles Collection of particles with a size distribution intermediate 

between those for small and large particles, having a median 

diameter between 50 and 100 μm.

PPG Pacific Proving Ground, renamed Enewetak Proving Ground in 

1958. 

Specific activity Radioactivity per unit mass (e.g., in curies per gram, or Ci g

−1

).

5. Method Description

Skin doses from dermal contamination resulted from depositions of mixed fission 

products on skin and clothing from descending and resuspended fallout, and from contact 

with contaminated surfaces. The specific skin dose pathways addressed in this standard 

method are:

 Deposition of descending fallout on skin and clothing

 Deposition of resuspended fallout on skin and clothing

 Direct transfer of contaminants from surface to skin

 Indirect transfer of contaminants from surface to skin (i.e., transfer from surface to 

hand, followed by transfer from hand to skin site).

Notice that skin doses from fallout deposited in the environment, e.g., “shine” from 

ground-deposited fallout and other contaminated surfaces, are discussed in SM ED03.
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5.1 General Approach for Skin Contamination

The dose (rad) at depth x in the skin, accrued during the time interval t1 to t2 (hours) from 

radionuclides deposited on the skin, is given by:



  

end

start

t

t

D(x) Cskin(t) DCFskin(x,t) dt

(1)

where

Cskin(t) = Activity concentration on the skin surface (Ci m−2) at time t (h)

DCFskin(x,t) = Skin dose conversion factor for x and t (rad h

−1 Ci−1 m2

) (See 

Table 1 for values

tstart = Time after detonation of the onset of dermal contamination (h)

tend = Time after detonation that the dermal contamination is removed (h)

If the activity on the skin surface was mixed fission products produced in a nuclear 

detonation, all times are measured relative to the time of the detonation.

For most dermal contamination scenarios, DCFskin(x,t) is only weakly dependent on time

over the duration of exposure. In such cases, the dependence on time can be suppressed 

and Equation 1 simplifies to:





end

start

t

t

D(x) DCFskin(x) Cskin(t) dt

(2)

The skin dose conversion factor, which is independent of the deposition mechanism, is 

discussed in the following section. The activity concentration on the skin, which is 

dependent on the deposition mechanism, is addressed for each pathway in subsequent 

sections.

5.2 Skin Dose Conversion Factor

Radiation transport techniques were employed to calculate DCFskin(x,t) for dermal contact 

with mixed fission products from a nuclear detonation. Beta and gamma emission spectra 

for fast fission of U-235, taken from Finn et al. (1979), were used to define the source 

terms in the one-dimensional electron-photon transport code CEPXS (Lorence et al., 

1989). Skin is assumed to have the composition and density (1.09 g cm−3) specified in 

Woodard and White (1986). The values of DCFskin(x,t) thus derived are provided in 

Table 1 in units of rad h

−1 Ci−1 m2

for time t ranging from 1 hour to 2 years after 
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detonation and for depth x up to 400 μm. Self-shielding of the skin-deposited particles 

has been neglected in this analysis.

Table 1. Skin Dose Conversion Factor DCFskin(x,t) (rad h

−1 Ci−1 m2

)

The basal cell layer between the epidermis and the dermis is considered the target organ 

for stochastic effects such as skin cancer. The depth of the radiosensitive basal cells 

varies with anatomical location, ranging from 20 to 100 μm over much of the body 

(ICRU, 1997). The average depth of the basal cell layers of the face, forehead, neck, 

shoulders, torso, and upper legs is 40 μm, while the average depth in the forearms and 

lower legs is 80 μm. The largest thickness of the epidermis is found on the palms of the 

hands and soles of the feet. These regions also exhibit the largest variation in thickness 

from area to area. While the “horny pads” of the palms and soles can be as much as

600 μm thick, in other areas the thickness can be as low as 200 μm. A thickness of 

400 μm is generally accepted as an average for these sites (Apostoaei and Kocher, 2010).

An expedient approach often used in dermal contact dose reconstruction is to ignore the 

time dependence of the skin dose conversion factor over the period of exposure, thus 

allowing the use of Equation 2, and to express DCFskin(x) with the equation:

DCFskin(x) = 900 ∙ SDMF(x) (3)

where

SDMF = Skin dose modification factor (See below for values)

900 = Nominal value of skin dose conversion factor DCFskin

(rad h

−1 Ci−1 m2

) (Barss, 2000)

Time t Depth x (μm)

(hours) 10 20 30 40 50 60 70 80 90 100 400

1 1280 1130 1040 970 910 860 830 790 760 730 410

2 1290 1130 1030 960 910 860 820 790 760 730 400

4 1290 1130 1030 960 900 850 810 780 750 720 390

6 1300 1130 1030 960 900 850 810 780 750 720 380

12 1300 1130 1030 950 890 840 800 770 740 710 370

24 1330 1140 1020 940 870 820 780 740 710 680 320

48 1350 1140 1010 920 850 800 750 710 670 640 270

72 1370 1140 1000 910 840 780 730 690 650 620 240

168 1380 1140 990 890 820 750 700 660 620 590 190

336 1380 1140 990 890 820 750 700 660 620 590 190

720 1380 1140 1000 900 820 760 710 660 630 590 210

1440 1380 1140 990 890 810 750 700 660 620 580 200

2880 1380 1130 990 880 810 740 690 640 600 570 190

4320 1380 1130 990 880 810 740 690 640 610 570 190

6480 1370 1130 990 890 810 750 700 650 610 580 210

8640 1360 1130 990 890 820 760 710 660 630 590 220

17280 1350 1130 1000 900 830 770 720 680 640 610 240
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The “skin dose modification factor” SDMF(x) adjusts the nominal value of 900 rad h

−1

Ci−1 m2according to the depth of the basal cell layer at the target skin site. Based on the 

data in Table 1, specific skin site values of SDMF have been estimated and are shown in 

Table 2.

Table 2. Recommended Values for SDMF

Skin Site SDMF

Face, behind ears*, forehead, neck, 

shoulders, chest*, torso, under belt*, and 

upper legs

1.3

Back of neck*, forearms, lower legs, and 

under boot edge* 0.9

Scalp*, palms of hands, backs of hands*,

and soles of feet 0.3

* SDMF values for these skin sites are not available in Apostoaei and Kocher

(2010). The indicated values are recommended based on similar skin thickness or 

proximity to other sites on the body.

5.3 Skin Dose from Descending Fallout

Unsheltered personnel (i.e., those outdoors on land and topside on a ship) during periods 

of fallout deposition were exposed to an accumulation of contaminants on their skin. The 

activity concentration (in Ci m−2) on a land surface or weather deck of a ship during a 

fallout event is represented by a time-dependent function Csurf(t), where t is the time after 

detonation. For an unsheltered individual, some fraction Fdes of the descending activity

(designated the “effective interception and retention fraction”) was intercepted by and 

retained on his skin. Thus, the activity concentration on his skin can be expressed by the 

equation:

skin surf Fdes C (t) C (t)

(4)

where

Csurf(t) = Surface activity concentration (Ci m−2)

Fdes = Effective interception and retention fraction

Methods for estimating Csurf(t) and Fdes are presented in the following sections.
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5.3.1 Surface Activity Concentration – Csurf(t)

The surface activity concentration at the location occupied by the individual during the 

deposition period is estimated from the measured or reconstructed intensity I(t) in that 

vicinity. This is accomplished through the use of time-dependent ratios of the intensity 

(R h

−1

) above an infinite, planar surface to the activity density (Ci m−2) of mixed fission 

products on that surface. Designated here as FR(t) , these shot-specific ratios were 

generated with the FIIDOS code (Raine et al., 2007) and are available in Appendix H of 

this SOP Manual. In this formulation, the surface activity density is given by:

C (t ) GSMF FR(t ) I(t ) surf   

(5)

where

GSMF = Gamma source modification factor

FR(t) = Time-dependent, shot-specific surface activity–intensity ratio

(“FIIDOS Ratio”) for an infinite plane estimated using FIIDOS; 

historically called 

(t)

I

SA

(Ci m−2 per R h

−1

)

I(t) = Intensity (R h

−1

)

The factor GSMF (gamma source modification factor) corrects for the fact that the 

contaminated surface was not infinite in spatial extent, as assumed in the FIIDOS 

calculations that generated FR(t). For land-based applications, the area of fallout 

deposition was generally large enough that the correction is insignificant, Thus, for

exposures to fallout on land, GSMF is set equal to 1. However, for shipboard exposure 

scenarios, the contaminated area was limited to the weather deck of the ship and the 

correction is necessary. Average values of GSMF for various types of ships are given in

SM ID01.

5.3.2 Effective Interception and Retention Fraction – Fdes

Apostoaei and Kocher (2010) developed a method of estimating the accumulation of 

radioactive particles on the skin of an unsheltered individual exposed to descending 

fallout. The method is based on a study of the interception and retention of particles of 

volcanic ash on the skin of humans in the aftermath of eruptions of the Irazu Volcano in 

Costa Rica in 1965 and 1966. The measured interception and retention fractions deduced 

from that study are modified by a number of adjustment factors to account for differences 

between the conditions under which that experiment was conducted and the conditions

appropriate for descending fallout scenarios. Thus, Fdes can be expressed as the product 

of four factors with the equation:
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Fdes R PS  EM  EF

(6)

where

R = Measured interception and retention fraction

PS = Particle size factor

EM = Moisture factor

EF = Enrichment factor

The R is the ratio of the mass per unit (skin) area deposited on skin to the mass per unit 

(ground) area deposited on the ground surface, as determined from the set of volcanic ash 

measurements.

The PS is an adjustment factor which accounts for the dependence of retention 

probability on particle size for material impacting the skin, and the difference between 

the particle size distribution at a fallout location of interest and the volcanic ash particle 

size distribution for which R was measured.

The EM is an adjustment factor that accounts for increased retention efficiency due to 

moisture on skin and/or particles. 

The EF is an adjustment factor that accounts for the difference between the specific 

activity (Ci g−1) of fallout particles retained on skin and the specific activity of fallout 

particles on the ground.

The brief discussions of these factors in subsequent subsections are largely summaries of 

more detailed presentations given by Apostoaei and Kocher (2010).

5.3.2.1 Measured Interception and Retention Fraction – R

The values of R, as determined from the volcanic ash data, are generally less than unity

since the skin on most areas of the body cannot retain a mass of descending contaminant 

per unit area larger than that found on the ground surface. R may exceed 1; however, for

special regions of the body (designated as “build-up barriers”) where descending 

contaminants may be collected and retained. Examples of build-up barriers include the 

back of the neck under the collar, under the belt, under a boot edge, and behind the ears. 

The values of R used for skin dose reconstruction are provided in Table 3. In addition to 

the best estimates (deterministic values) of R for the various body regions, the table also 

provides the corresponding 95th percentile upper bounds. For body locations not listed in 

Table 3, the parameters for the scalp are used as defaults.
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Table 3. Interception and Retention Fraction (R)

Skin Site Deterministic Value* 95th Percentile

Upper Bound*

Face, neck†, shoulders, back and sides of 

torso, forehead, palms of hands, and soles of 

feet†

0.015 0.12

Chest (unspecified amount of hair) 0.03 0.28

Forearms, backs of hands†, upper legs, and 

lower legs (above boot edge) 0.06 0.36

Scalp 0.23 1.0

Back of neck under collar, under belt, under 

boot edge, and behind ears 1.5 5.0

*

Interception and retention fractions and upper bounds were taken from Apostoaei and Kocher (2010).

†

Interception and retention fractions for these skin sites are not available in Apostoaei and Kocher (2010). The 

indicated values are recommended based on similarity to other sites. 

5.3.2.2 Particle Size Factor – PS

The likelihood that an intercepted particle is retained on the skin depends primarily on the 

particle’s size. Particles with diameters less than about 50 μm have nearly equal 

probabilities of retention, while those with diameters greater than 50 μm have retention 

probabilities which are inversely proportional to particle diameter. Thus, the interception 

and retention fractions must be adjusted to account for the fact that the particle size 

distributions of the descending fallout to which individuals were exposed differed from 

the size distribution of volcanic ash for which the data was taken. 

It was observed in the volcanic ash study that 30–40 percent of the total ash mass 

consisted of particles with diameters less than 50 m (Apostoaei and Kocher, 2010, 

Figure 4-1). If the fraction of mass composed of particles with diameters less than 50 μm 

in a specific instance of descending fallout is known to have been fdes, an estimate of the 

PS factor is obtained by simply taking the ratio of the two fractions using the equation:

PS  f

des / 0.3

(7)

Most often, however, size distribution data for specific fallout events are not available, In 

this case, the distribution must be characterized from less direct information. Figure 1

(taken from Glasstone and Dolan, 1977) is useful in estimating the size of particles that 

reached the ground at a given time after detonation (abscissa) from a given altitude 

(ordinate). Applying this to a fallout event, the relevant time is the time after detonation 

that fallout occurred at the location of interest, and the relevant altitude is the stabilized 

height of the bottom of the radioactive cloud. This height is about 30,000 feet for a 
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typical nuclear detonation; more specific values are available for many shots in 

Hawthorne (1979). Note that particle size is given as radius in this graph. 

Figure 1. Fall Times of Particles of Different Sizes from Various Altitudes

(Also shown is the typical percentage of activity in each particle size class)

As an example, consider fallout from Operation GREENHOUSE, SHOT DOG at 

Enewetak Island. The fallout started about 2 hours after detonation and the intensity 

peaked about 3 hours later before subsiding (Thomas et al., 1979). The bottom of the 

cloud stabilized at 33,000 feet within minutes after detonation (Hawthorne, 1979). From 

Figure 1 (for time = 5 hours and altitude = 33 kft), the particles that contributed to this 

fallout event mostly had diameters of 2 × 47 μm = 94 μm or greater. This is consistent

with the observation in Cooney, 1951 regarding the size of these fallout particles and 

characterizes this as large particle fallout, as defined in Section 4. Again referring to 

Figure 1, most particles with diameters of 50 μm or less would not have reached the 

ground until at least 16 hours after the detonation. 

Fallout on the residence islands of Enewetak Atoll during Operation HARDTACK I was 

dominated by the combined depositions from Shots FIR and KOA about 2 days after the 

Shot FIR detonation and 1 day following Shot KOA. It is evident from Figure 1 that this 

fallout consisted predominantly of small particles and therefore is characterized as small 

particle fallout, per Section 4.

As a general rule of thumb, in the absence of more specific particle size information,

 For fallout composed of small particles, use PS = 1.3 and a 95th percentile upper 

bound of 1.6.
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 For fallout composed of large particles, use PS = 0.8 and a 95th percentile upper 

bound of 1.0. 

 For fallout composed of intermediate particles, use PS = 1.0 and a 95th percentile 

upper bound of 1.5. 

Note: The small, large, and intermediate particle classes are defined in Section 4.

5.3.2.3 Moisture Factor – EM

Retention of particles on the skin is enhanced if the skin and/or the incident particles are

moist. The volcanic ash data were collected in the mild, humid climate of Costa Rica. 

Participants of testing at the Pacific Proving Ground (PPG) operated in a warm climate 

that was as humid as, and at times more humid than, that of Costa Rica. Therefore, the 

mean and 95th percentile upper bound of EM used for PPG exposures are 1.2 and 1.5, 

respectively. The climate at the Nevada Test Site (NTS) in the early morning when most 

of the testing took place was cool and dry. Consistent with this, the mean and 95th

percentile upper bound of EM used for NTS exposures are 0.75 and 1.0, respectively.

5.3.2.4 Enrichment Factor – EF

Studies indicate that the specific activity (i.e., activity per unit mass) of fallout particles

on skin can be greater than the specific activity of fallout particles on the ground. An

“enrichment factor” is defined as the ratio of these specific activities. This effect can be 

understood as follows. If radionuclides were distributed uniformly throughout the 

volumes of all particles, the specific activity would be independent of particle size and no 

enrichment would take place. In the process of particle formation after a nuclear 

detonation, however, fractionation of radionuclides occurs: some radionuclides (mainly 

those of refractory elements such as zirconium, niobium, and cerium) tend to be 

volumetrically distributed in larger particles while others (mainly those of volatile 

elements such as cesium, strontium, and iodine) tend to be distributed on the surfaces of 

smaller particles. The specific activities of the smaller, surface-coated particles are 

generally greater than those of the larger particles. As discussed previously, the

probability of particle retention on the skin is also greater for smaller than larger 

particles. This correlation between specific activity and retention probability produces the 

enrichment effect.

Fallout at locations relatively close to ground zero (e.g., those within the boundaries of 

the NTS) consisted of large particles, as defined in Section 4. Most of these particles 

contained predominantly refractory elements that were volumetrically distributed, which

by themselves would have produced no enrichment. However, volatile radionuclides 

coalesced on the surfaces of the smaller particles in the fallout distribution, and this 

small-particle component created the potential for significant enrichment. For exposure to 

large-particle descending fallout, the mean and 95th percentile upper bound of EF are set 

to 2.5 and 3.5, respectively.
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At locations far from ground zero (e.g., most residence sites at PPG), fallout consisted of

small particles that had a higher proportion of volatile radionuclides deposited on their

surfaces and relatively high specific activities. Nevertheless, it is expected that only a 

modest amount of enrichment occurred there because most of the radionuclides were 

entrained in small particles, and these particles were retained on skin with roughly the 

same efficiency. Therefore, the mean and 95th percentile upper bound of EF used for 

small particle fallout are 1.3 and 1.8, respectively.

For exposure to descending fallout composed of intermediate particles, the mean and 95th

percentile upper bound of EF are taken as 2.0 and 3.7, respectively.

5.3.3 Skin Dose Calculations for Descending Fallout 

A composite expression for calculating the skin dose accrued during the time interval t1

to t2 from dermal contact with descending fallout is obtained by combining Equation 1

with Equations 4 through 6 and gives the equation:



       

2

1

( ) ( ) ( ) ( , )

t

t

skin des t DCF x t dt

I

SA D x R PS EM EF GSMF I t

(8)

where

Ddes(x) = Absorbed dose to skin at depth x from descending fallout (rad)

All factors in this equation are defined and discussed above. Values of DCFskin(x,t) from 

Table 1 can be used in Equation 8, or the approximate methods of Equations 2 and 3 can 

be employed to move this factor outside the integral. Intensity I(t) is formulated on the 

basis of measurements or reconstruction. The shot-specific functions FR(t) are available 

in SOP Appendix H. GSMF is addressed in Section 5.3.1. The factors R, PS, EM, and EF, 

the product of which is the effective interception and retention fraction Fdes, are discussed 

and quantified in subsections 5.3.2.1–5.3.2.5, respectively; means and 95th percentile 

upper bounds of these parameters are summarized in Table 3 and Table 4.
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Table 4. Summary of Factors in the Calculation of Fdes

Parameter Deterministic 

Value

95th Percentile 

Upper Bound

R: Interception and Retention Fraction See Table 2 See Table 2

PS: Particle Size Factor*

Small particles 1.3 1.6

Large particles 0.8 1.0

Intermediate particles 1.0 1.5

EM: Moisture Factor 

 Pacific Proving Ground 1.2 1.5

Nevada Test Site 0.8 1.0

EF: Enrichment Factor

Small particles 1.3 1.8

Large particles 2.5 3.5

Intermediate particles 2.0 3.7

*Operation-specific values should be used when available.

5.4 Skin Dose from Resuspended Fallout

Dermal contamination resulted not only from descending fresh fallout, but also from 

previously deposited fallout that was resuspended in the air and subsequently deposited 

on the skin. Resuspension occurs as a natural phenomenon (i.e., wind-driven 

resuspension) and as a result of human activities (e.g., pedestrian and vehicular traffic, 

helicopters operations). An individual who worked or resided in a region where fallout 

had been previously deposited (referred to as a “fallout field”) is assumed to have been 

exposed to resuspended fallout for the duration of time he spent outside (or topside), 

Even after his exposure to resuspended fallout ended when he relocated to an 

uncontaminated area (e.g., by going inside or below deck), the radioactive contaminants 

that had accumulated on his skin remained there until later removed, usually by washing. 

The analysis of skin dose from these exposures is more involved than that which led to 

Equation 8 for descending fallout, and is addressed in an NTPR technical memorandum

(Weitz, 2011). Initial steps in this analysis include determination of the airborne activity 

concentration (Cair(t)) and the development of an effective interception and retention 

factor Fres for the resuspension scenario.

5.4.1 Airborne Activity Concentration Cair(t)

For large areas that are relatively uniformly contaminated, the airborne activity 

concentration within a few meters of the contaminated surface can be related to the 

surface activity concentration with the equation: 

C (t) C (t) K(t') air surf  

(9)
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where

Cair(t) = Concentration in air (Ci m−3)

K(t) = Resuspension factor (m−1)

t = Time after detonation (h)

t' = Time after end of fallout (h)

In most cases, the radiation intensity peaked at the end of fallout deposition, so t' is 

usually referenced to the time of the peak intensity. If Δt is the time interval (hours) from 

detonation to peak intensity at the location of interest, then t' = t - Δt.

After a fallout episode, the fraction of material deposited on the ground surface that is 

available for resuspension decreases with time due to downward migration of fallout 

particles and other fallout-soil attachment processes. The following equation (USNRC, 

1983) models this effect and provides the basis to calculate time-dependent resuspension 

factors for land-based long-term exposures of personnel at the PPG or NTS with the 

equation:

24 9 1

'

0.01 5

( ') 10 10 m

 

 



  

t

K t e

(10)

In addition, values of K for specific short duration activities, such as troop maneuvers 

involving helicopter operations in contaminated areas, aircraft decontamination, trucking, 

digging trenches, etc., are provided in Table A3-1 in SM ID01.

The flux of airborne contaminants is given by the equation:

(t) V C (t) air air   

(11)

where



air(t) = Flux of airborne activity (Ci m−2

s

−1

)

V = Average velocity of resuspended contaminants (see below) (m s

−1

)

In this expression, V is assumed to be the wind speed if the movement of contaminants 

was primarily induced by the wind. On the basis of meteorological data, wind speeds of 

5 m s

−1

and 4 m s

−1

are normally assumed for PPG and NTS, respectively. For an 

individual walking in a contaminated area on an essentially windless day, where the 
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resuspension is driven primarily by mechanical disturbance (i.e., the action of walking),

an average deposition velocity of 1 m s

−1

applies. Deposition velocities can reach 7 to 

14 m s

−1

if exposure occurs while riding in the back of a truck moving at 15 to 30 mile 

per hour (Apostoaei and Kocher, 2010). The uncertainties in these velocities are included 

in the 95th percentile upper bound of the collection efficiency (CE) reported in Table 5. 

5.4.2 Effective Retention Fraction – Fres

If an airborne activity flux 

(t) air

is incident on bare skin, the amount of activity per unit 

area intercepted by the skin during an incremental time interval from t to t + dt is

t dt air  ( )

(Ci m−2). Only a fraction Fres (“effective retention fraction”) of this activity 

will stick to the skin. Thus, the incremental amount of contamination dCskin(t) retained on 

the skin during this interval is given by the equation:

t K(t') dt

I

SA dC (t) F φ (t) dt F V GSMF I(t skin res air res

 3600     3600     ) ( )  (12)

where

Fres = Effective retention fraction

Equations 5, 9, and 11 have been utilized to obtain the second expression. The factor 

3600 converts from hours to seconds.

Borrowing from the development in Section 5.3.2 of an analogous parameter for the 

retention of descending fallout, Fres is expressed as the product of five factors: 

PS EM EF

R

R

F CE

fa

res      (13)

where

CE = Collection efficiency

R/Rfa = The ratio of R, the interception and retention fraction for the skin 

site of interest to the fraction (Rfa) determined from those studies 

for the bare forearm 

PS = Particle size fraction

EM = Moisture factor

EF = Enrichment factor
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The CE fraction is the fraction of particles incident on bare skin that are retained on the 

skin, as determined by wind tunnel studies. The largest value reported for this parameter 

(Asset and Pury, 1954) is 0.02, based on an experiment in which wind-driven small 

particles (almost all less than 50 μm in diameter) were incident on a bare forearm. This 

value is taken as both the mean and the 95th percentile upper bound for CE. This 

approach differs from that of Apostoaei and Kocher (2010), who apply the volcanic ash 

data to resuspended fallout as well as to descending fallout.

The R/Rfa ratio was derived from the volcanic ash studies with values for R given in 

Table 3 and an estimated Rfa value of 0.06. This ratio allows the collection efficiency to 

be estimated for body sites other than the forearm.

The PS fraction is the fraction of resuspended fallout particles that have diameters less 

than 50 μm, divided by the fraction of particles used in the referenced wind tunnel 

experiment that had diameters less than 50 μm. The latter fraction is very nearly one. The

size distribution of resuspended particles has not been studied, but it is certain to be 

dependent on the magnitude of the disturbance causing the resuspension. If that 

disturbance is light wind, the particle size distribution will consist mostly of small 

particles (those with diameters less than 50 um), so PS ≈ 1. If the disturbance is strong 

(e.g., strong wind or mechanical disturbance such as vehicular traffic), the lofted 

particulates will contain some intermediate and even large particles, making PS less 

than 1. In the limiting case of a very strong disturbance (e.g., blast wave or helicopter 

takeoff/landing), the size distribution of resuspended particles may even approach that of 

the deposited fallout. Given the uncertainty associated with this parameter, the high-sided 

assumption is made that PS = 1.

The EM factor is an adjustment factor that accounts for an increase in collection 

efficiency due to moisture on skin and/or particles. The mean of EM is taken as 3.0 with a 

95th percentile upper bound of 3.9 for resuspension in PPG because the wind tunnel data 

were collected under dry conditions. The mean and 95th percentile upper bound used for 

NTS exposures are 1.0 and 1.3, respectively

The EF factor is an adjustment factor that accounts for the difference between the 

specific activity (Ci g−1) of fallout particles retained on skin and the specific activity of 

resuspended particles. EF for resuspended material is assumed to have a mean value of 

1.0 and a 95th percentile upper bound of 1.3.

5.4.3 Skin Dose Calculations for Resuspended Fallout

Consider the scenario of an individual exposed to resuspended fallout from a time tstart to 

a later time tend, during which contaminants were continuously deposited on his bare skin. 

The accumulated contaminants then remained on his skin from tend until they were 

removed by washing at twash. All times are in hours after detonation. It is shown in Weitz 

(2011) that, on the basis of Equations 1 and 12, the following expression for the dose at 

depth x in the skin from contact with resuspended fallout is obtained.
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Dres(x) = 3600 ∙ V ∙ Fres ∙ GSMF

∙ {∫ K(τ − Δt)

tend

tstart

∙ [∫ FR(t) ∙ I(t) ∙ DCFskin(x,t) ∙ dt

twash

τ

] dτ}

(14)

where

twash = time after shot that contamination was removed by washing (h)

Values of DCFskin(x,t) from Table 1 can be used in Equation 14, or the approximate 

methods of Equations 2 and 3 can be employed to move this factor outside the integrals. 

Intensity I(t) is formulated on the basis of measurements or reconstruction; the shotspecific functions FR(t) are available in SOP Appendix H; and GSMF is addressed in 

Section 5.3.1. Estimates of K(t) and V are provided in Section 5.3.1. The factors 

comprising Fres are discussed and quantified in subsections 5.4.2; means and 95th

percentile upper bounds of these parameters are summarized in Table 5. Values for tstart, 

tend, and twash are selected on the basis of the type and schedule of work performed by the 

individual.

Table 5. Summary of Factors in the Calculation of Fres

Parameter Deterministic 

Value

95th Percentile 

Upper Bound

CE: Collection Efficiency 0.02 0.06

R/Rfa: Ratio of Interception and 

Retention Fractions for 

Descending Fallout

See Table 3 See Table 3; upper bound of R for 

forearms, backs of hands, and 

upper/lower leg is set equal to 0.06, 

i.e., no error for resuspension

PS: Particle Size Factor 1.0 1.0

EM: Moisture Factor 

Pacific Proving Ground 3.0 3.9

Nevada Test Site 1.0 1.3

EF: Enrichment Factor 1.0 1.3

In many scenarios of interest, the time-dependent functions I(t), K(t'), FR(t), and 

DCF(x,t) vary negligibly during the time interval tstart → twash. In this case, these 

functions can be replaced by their average values over that time interval in the equation:

( ) 3600 ( ) [ ( ) ]

2

res wash res res res D x  V  F GSMFGI K  DCF x  1⁄2 t  t t

(15)
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where

I , = Average intensity (R h

−1

)

K , = Average resuspension factor (m−1

)

G = Average ratio of surface activity to intensity. (Ci m−2 R

−1

)

DCF (x) = Average skin dose conversion factor (rad Ci−1

)

Δtres = The duration spent in the fallout field (tend – tstart) (h)

Δtwash = The time interval from exiting the fallout field to removing the 

deposited contaminants from the skin by washing (twash – tend) (h).

Equations 14 and 15 represent single-day exposures to resuspended fallout. Often an 

individual resided and/or worked for an extended period in a fallout field, and 

consequently was exposed repeatedly to resuspended fallout. On a ship, these exposures 

were limited to 4 days after the end of shipboard deposition in the present model, since 

the resuspension factor is assumed to have been zero after that time. On land, the cycle 

was repeated daily until personnel permanently departed from the test site. These 

scenarios are accommodated by applying Equation 14 or 15 to each day’s exposure and 

summing the daily skin doses.

5.5 Skin Dose Calculations from Prior Detonations

Dermal contamination due to resuspension of previously deposited (“old”) fallout by the 

thermal pulse or blast wave produced in a detonation at NTS (an acute event) can be 

estimated by assuming that a fraction of the activity on the ground is resuspended and 

then redeposited in roughly the same area. Thus, skin dose due to exposure to 

resuspended old fallout by a thermal pulse or blast wave is calculated in a manner 

analogous to that due to descending fallout (Apostoaei and Kocher, 2010). The dose 

produced by old fallout is given by:

D t x f f C t F DCF x t t

old ( old , )  [ R



D



surf( old )]des

 ( ,

old )

(16)

where

Dold(told,,x) = Dose from old fallout (rad)

told = Time after the detonation (h)

In this equation, the surface activity density of old fallout Csurf(t) is evaluated with 

Equation 5, the effective interception and retention fraction Fdes with Equation 6, and the 
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skin dose conversion factor DCF(x,t) with Table 1 or Equation 3; t is the duration of 

exposure (h).

The (unitless) parameter fR represents the fraction of activity on the ground that is 

resuspended and remains in the air at the time deposition on the skin occurs. The 

resuspension factor, fR, can be estimated as follows:

fR K H

(17)

where

fR = Resuspension fraction

K = Resuspension factor (m−1)

H = Height of a layer of air were radionuclides are uniformly 

distributed (m)

For personnel such as forward observers who were impacted by dust resuspended by a 

blast wave at the time of detonation, a reasonable mean value of K is 10−4 m−1, with a 95th

percentile upper bound of 10−3 m−1. Typically, H is on the order of 100-300 m (Barrett et 

al., 1986).

In addition, fD is a (unitless) dispersion factor that accounts for the fact that the activity 

resuspended by a nuclear detonation can be spread over a larger area around ground zero 

than it originally occupied. When a dispersion factor applies, it is estimated by assuming 

a blast wave resuspended material from a circle with a radius R1 and dispersed it over a 

circle with a larger radius R2. If the initial concentration of material on the ground was 

uniform and the resuspended material is assumed to have been dispersed uniformly by 

the blast wave, the dispersion factor is given by the ratio of the areas of the two circles. 

Therefore, if R2 is twice R1, the dispersion factor is (R1/R2)

2 = 0.25.

In considering exposure to radionuclides in old fallout resuspended by a detonation, it is 

important to distinguish between (1) individuals designated as forward observers and 

located in the blast-wave region at the time of detonation and (2) individuals (e.g., 

maneuver troops) entering the blast-wave or precursor region at some time after a 

detonation. The important difference is that forward observers were exposed to 

resuspended fallout particles of all sizes, whereas individuals who entered the blast-wave 

or precursor region after a detonation were exposed only to small resuspended particles, 

because larger particles (i.e., particles with diameters greater than about 100 μm) were 

redeposit quickly and were not present in the air at the time of exposure. Another 

important difference is that forward observers were exposed in a very short period of time 

(acute exposure), while maneuver troops generally spent a longer period of time (up to 

hours) in lingering clouds in the blast-wave or precursor region. Therefore, Equation 16

is used to assess doses for forward observers from exposures to particles resuspended by 
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the blast wave. Doses for maneuvering troops are calculated using the equations in 

Section 5.4.

6. Data and Input

Operation and shot-specific data are compiled in SOP Appendices A–C. 

7. Referenced SOPs and Standard Methods from this Manual

(1) SOP RA01 - Radiation Dose Assessment for Cases Requiring Detailed Analysis

(2) SM ED03 - Skin Dose from External Sources

(3) SM ID01 - Doses to Organs from Intake of Radioactive Materials

8. References

Apostoaei, I., and Kocher, D.C., 2010. Radiation Doses to Skin from Dermal Contamination. 

DTRA-TR-09-16, Defense Threat Reduction Agency, Fort Belvoir, VA. October 28.

Asset, G., and Pury, D., 1954. “Deposition of Wind-Borne Particles on Human Skin,” American 

Medical Association Archives of Industrial Hygiene and Occupational Medicine, 

Volume 9, Number 4.

Barret, M., Goetz, J., Klemm, J., McRaney, W., and Phillips, J., 1986. Low Level Internal Dose 

Screen-Conus Tests. DNA-TR-85-317, Defense Nuclear Agency, Washington, DC. 

Barss, N.M., 2000. Methods and Applications for Dose Assessment of Beta Particle Radiation.

SAIC - 001/2024, Science Applications International Corporation, McLean, VA. 

January 31.

Cooney, J.P., 1951. Operation GREENHOUSE Scientific Director’s Report, Annex 9.3:

Radiological Safety. WT-89, Armed Forces Special Weapons Project, Washington, DC.

DoD (Department of Defense), 2020. “Guidance for the Determination and Reporting of Nuclear 

Radiation Dose for DoD Participants in the Atmospheric Nuclear Test Program (1945-

1962).” Title 32, Code of Federal Regulations, Part 218. Washington, DC. July 1.

Finn, S.P., Simmons, G.L., and Spencer, L.V., 1979. Calculation of Fission Product Gamma Ray 

and Beta Spectra at Selected Times after Fast Fission of U238 and U235 and Thermal 

Fission of U 235. SAI-78-782-LJ/F Report, Science Applications, Inc., San Diego, CA.

Glasstone, S., and Dolan, P.J., 1977. The Effects of Nuclear Weapons, 3rd Edition. U.S. 

Department of Defense and U.S. Department of Energy.

Hawthorne, H.A. (editor), 1979. Compilation of Local Fallout Data from Test Detonations 

1945–1962, Extracted from DASA 1251: Volume I – Continental U.S. Tests,

DNA 1251-1-EX, and Volume II – Oceanic U.S. Tests, DNA 1251-2-EX. Defense 

Nuclear Agency, Washington, DC.
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ICRU (International Commission on Radiation Units and Measurements), 1997. Dosimetry of 

External Beta Rays for Radiation Protection. ICRU Report 56, International Commission 

on Radiation Units and Measurements, Bethesda, MD.

Lorence, L.J., Morel, J.E., and Valdez, G.D., 1989. User’s Guide to CEPXS-ONEDANT: a OneDimensional Coupled Electron-Photon Discrete Ordinates Code Package, Version 1.0. 

SAND 89-1661, Sandia National Laboratories, Albuquerque, NM. 

Raine, D.A. III, Egbert, S.D., Stiver, J.H., and Case, D.R., 2007. FIIDOS – A Computer Code for 

the Computation of Fallout Inhalation and Ingestion Dose to Organs, Computer User’s 

Guide, (Rev. 4). DTRA-TR-07-11, Defense Threat Reduction Agency, Fort Belvoir, VA.

May 30.

Thomas, C., Gminder, R., Stuart, J., Weitz, R., Goetz, J., and Klemm, J., 1982. Analysis of 

Radiation Exposure for Naval Personnel at Operation GREENHOUSE. DNA-TR-82-15, 

Defense Nuclear Agency, Washington, DC.

USNRC (United States Nuclear Regulatory Commission), 1983. Radiological Assessment – A 

Textbook on Environmental Dose Analysis. NUREG/CR-3332, Nuclear Regulatory 

Commission.

Weitz, R.L., 2011. Skin Dose from Dermal Contact with Resuspended Material. NTPR-TM-11-

02, Defense Threat Reduction Agency, Fort Belvoir, VA. July 1. 

Wood, H. Q., and White, D. R., 1986. “The Composition of Body Tissues,” British Journal of 

Radiology 59:1209-1218.