Impact

DOE-HDBK-3010-94

4.0 Solids; Powders

Figure A.39 in Appendix A. The size distribution of the soil is shown in Figure A.40 and

tabulated in Table A.44. The soil was deagglomerated and pumped into the wind tunnel at

speeds of 1.4-, 4.6-, 6.8- and 8.9-m/s (3.1, 11, 15 and 20 mph). The results are plotted in

Figure 4-20, taken from the referenced source. The fraction airborne, ARF, is:

ARF = 0.0134 U + 0.00543

(4-2)

where U = windspeed, m/s.

The RF measured at various windspeeds, shown in Table 4-14, ranges from 0.44 at 1.4 m/s

to 0.90 at 8.9 m/s. The ARF at 8.9 m/s is 0.125 and, using the measured RF, 0.90, the

fraction of soil less than 10 m diameter is ~ 0.113. The fraction of the soil <10 m

diameter listed in Table A.43 is 0.00088. It would appear that a large mass of smaller

particles was shed by the larger soil particles or some fragmentation has occurred.

The equation would only apply to soil or powder with a similar size distribution and

characteristics. Process powders tend to be finer and more coherent and the observation here

may not be applicable. On the basis of the experimental measurements, a bounding ARF and

RF are assessed to be 0.0134 U + 0.00543 and 1.0 (limited by the total mass of material in

this size fraction in the source material) are recommended.

Table 4-14. Airborne Soil Particle Size Distribution

(Table 6 - Sutter, August 1980)

Wind Speed,

Aerodynamic

%10 m and

mph

Mass Median

less

Diameter, m

3.2

>10

10.4

6.7

15.2

9.8

20.0

5.3

4.4.3.3

Impact

Under some circumstances, powder at rest could be ejected into the air by the response of

the solid substrate on which the powder rests by the vibration/jolting induced by the impact

of falling debris or strong seismic vibrations. The effect could be minor for very solid

substrates such as structural members. The flexing of thin, metal sheets could be substantial

especially if the flexing is repetitive. Also the cohesiveness of the powder could inhibit

Page 4-83