Respirable Fraction (RF)

DOE-HDBK-3010-94

1.0 Introduction

controlled conditions. Attention is given to the parameters, if known, that may have a

significant influence upon suspension by the specific mechanism and the uncertainty in the

measurement as indicated by the variability of the results. Those applying the data must be

aware of the range of stress represented by the measured ARFs, and seek to define the

accident conditions to determine, in a gross sense, whether or not the stresses induced by the

postulated events are bounded by the experimental parameters as evaluated in this document.

It is important to note that the experiments discussed evaluate release phenomena holistically.

No attempt is made to precisely characterize total airborne material in terms of individual

mechanisms acting within an overall given release. To obtain useful data outside the

immediate physical chaos of the stress-inducing event itself, the experimental apparatus cited

almost uniformly relied upon designs to channel air to some contamination collection

mechanism a short distance from the point of generation. The need to keep this distance

small to avoid introducing new distortion in the form of aerosol deposition effects is one of

the reasons for the relatively small scale of many experiments.

In keeping with this experimental design, the interpretation of experimental data does not

consider material momentarily airborne from substrate mass ejection due to physical stresses

acting on the substrate mass as an aerosol suspended in air. For example, in fire and boiling

experiments, fuel mass and volumes of solution were observed to splatter or launch from the

experimental substrate and land on surfaces in the local vicinity. The radioactive

contamination carried with this material that deposits and is measured on the adjacent

surfaces is not an aerosol suspended in air, and does not travel on air currents. It represents

a source of highly localized migration that is not amenable to meaningful prediction and is

not relevant to the issue of how much material might be expected to escape the immediate

area and disperse in air.

Respirable Fraction (RF)

The RF is the fraction of airborne radionuclides as particles that can be transported through

air and inhaled into the human respiratory system and is commonly assumed to include

particles 10-m Aerodynamic Equivalent Diameter (AED) and less. Other definitions of

"respirable particles" have been presented by various groups at different times. The British

Medical Research Council adopted a definition in 1952 classifying particles with a terminal

velocity equal to that of a 5-m diameter as "respirable dust." The U. S. Atomic Energy

Commission defined "respirable dust" as insoluble particles that are part of inhaled dust

which penetrate to the non-ciliated portions of the gas exchange region, and with a 50%

respirable cut-size of 3.5-m AED. The American Conference of Governmental Industrial

Hygienists has adopted a definition that is almost identical, differing only in the 2 m

fraction allowed. The U. S. Environmental Protection Agency defines "inhalable dust"

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