GSI – Estimating Inhalation Intakes -1- SC&A –June 11, 2013 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

MEMO 

TO: Advisory Board on Radiation and Worker Health Work Group on TBD-6000 

FROM: John Mauro, Robert Anigstein, and Steve Marschke, SC&A 

SUBJECT: SC&A Commentary on “White Paper – Square Function Approximation to 

Estimating Inhalation Intakes,” Prepared by David Allen, DCAS, June 2013 

DATE: June 11, 2013 

Members of the Advisory Board, NIOSH, and SC&A have held numerous discussions regarding 

methods that can be used to assign a plausible upper bound to the airborne uranium dust loadings 

that workers might have experienced at General Steel Industries (GSI) during the years when 

GSI was handling uranium. Our discussions unfolded in two phases. The first phase was 

primarily concerned with selecting the appropriate surrogate uranium dust loading for GSI. The 

main concern was that no dust loading data were available for GSI, and it was necessary to make 

use of surrogate data taken from other facilities where uranium was handled in a similar manner. 

This was challenging because most of the dust loading surrogate data were available from 

facilities that were machining, rolling, grinding, extruding, etc., uranium, and where the dust 

loadings were implausibly high as applied to GSI. After some additional research, NIOSH 

identified a number of sites where uranium was handled much in the same manner as it was at 

GSI, and all participants agreed that these uranium dust loading data could be used as surrogate 

data for GSI. 

The second phase of discussion, which is the topic covered in this white paper, has to do with 

reconstructing the exposures to airborne uranium dust at GSI, recognizing that the exposures 

were intermittent, and not continuous, as they were at the facilities that were used as the source 

of the surrogate data. At GSI, after handling the uranium for the purpose of radiography, the 

uranium dust settles over some time period that depends on the settling rate of the uranium. 

However, while the dust is settling on surfaces and also during the time after the dust has all 

settled, there is residual uranium dust on surfaces that can be resuspended. Typically, the 

amount of airborne uranium dust associated with resuspension processes is small compared to 

the amount of airborne uranium dust associated with the actual handling of uranium. Hence, one 

would expect cycles of relatively high followed by relatively low concentrations of airborne 

uranium dust throughout the facility where uranium is periodically handled. This cyclic process 

is referred to as the “square wave function” in NIOSH’s white paper.

All parties have been struggling with how best to address this cyclic phenomenon in a 

scientifically sound, plausible, and claimant-favorable manner, and we believe that, in its current 

white paper, NIOSH has developed a simple, but elegant approach to addressing this complex 

problem. 

In their white paper, NIOSH begins from first principles, explaining that the airborne activity (A 

in Bq) can be described by a simple first order differential equation, where A at any point in 
GSI – Estimating Inhalation Intakes -2- SC&A –June 11, 2013

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution.

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

time, t in seconds, is a function of the production rate P in Bq/sec and the removal rate of the 

uranium, λ, in units of sec-1. Under such first order process, at times that are long compared to 

the rate of removal, the airborne inventory of uranium reaches equilibrium, and the equation 

reduces to A = P/λ. In NIOSH’s white paper, they point out that equilibrium may not be 

achieved during any given radiography campaign and the airborne activity at any given point in 

time during the handling of uranium is simply expressed as:

{1 exp( t)} PA 



   

At some time t1 (the term used in NIOSH’s white paper), the airborne activity will build up to a 

given level and then, when uranium handling ceases, uranium production ceases, and the 

airborne activity will begin to decline according to A = A(t1) * exp(-λ(t-t1)). Hence, the graph 

depicting the amount of airborne activity of uranium in the work area at any time following the 

beginning of the first uranium handling campaign will take the form shown in Figure 1 of the 

NIOSH white paper, reproduced below.

Figure 1 – Buildup and Decline of Airborne Activity from a Single Episode

Integrating under the curve will yield the total amount of airborne uranium (Bq-sec) over all time 

due to the handling of uranium over the time duration t = t1. Here is where the elegant nature of 

the NIOSH paper comes in. Attachment A of the NIOSH white paper demonstrates that the total 

amount of airborne uranium over infinity, expressed in units of Bq-sec, due to a single campaign 

that lasts for a time of t1 seconds (such as 15 minutes; i.e., 900 seconds) is simply P/λ*t1. Then, 

the total inventory of airborne uranium over all campaigns is simply P/λ*t1 times the number of 

such campaigns. 

The above discussion does not present specific concentrations, but we assume that NIOSH plans 

to use the upper 95th percentile concentration of uranium; i.e., A/V, where V is the volume of the 

space (m3) and 68.7 dpm/m3is the equilibrium dust loading (Allen 2013). Since the volume of 

the space is a constant, both sides of the above equations can be divided by the volume, and the 

equation solved for the airborne concentration, i.e., C = P/(V*λ)*t1.
GSI – Estimating Inhalation Intakes -3- SC&A –June 11, 2013

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution.

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

Given this understanding, SC&A agrees with NIOSH’s basic strategy. The only question that we 

need to discuss is the duration that uranium is handled during each radiography campaign. It is 

our understanding that NIOSH plans to assume 15 minutes. We also need to know the total 

number of campaigns during the time that uranium was undergoing radiography at the site. We 

believe that, at present, NIOSH is assuming that during each campaign, uranium is handled for 

about 15 minutes, and for the rest of the time that uranium is on site, it is not actually being 

handled in a manner that would generate uranium dust. This is a topic that will need to be 

discussed at the next work group meeting, along with the number of assumed campaigns. One of 

the challenges will be how to deal with the production of uranium dust when uranium is handled 

at times when it is not in the set-up and take-down mode for radiography; for example, when it is 

being brought onto the site, placed in storage prior to radiography, and being removed from the 

site. Does the 15 minutes of handling account for these other handling operations?

References

Allen, D., 2013. White Paper – “Square Function Approximation to Estimating Inhalation 

Intakes,” Prepared by David Allen, DCAS. June 2013.