home edit2 whole TSD November 2002 PDF format - OEHHA

ninety-five percent were diesel. This linear rise of dieselization may be expected to have produced a
linear rise of the national average exposure concentration around the trains. This linear rise is used in all
the more realistic exposure patterns.
The exposure of workers on trains would then generally have declined as the newer, less smoky
locomotives replaced the older, smokier locomotives on the main lines. To quantify the anecdotal
information of greater smokiness of locomotives in the period before 1960, the national average
exposure concentration was assumed to decline linearly in the second period, 1960-1980, to the
baseline measured in 1982-3. The decline assumed from 1959 to 1980 is consistent with the report of
sharp decreases of emissions of new engines between the 1970’s and the 1980’s. Emissions from
naturally aspirated four-stroke engines declined from 2.1-3.0 g/kW-hr in the 1970’s to 0.25 -0.6
g/kW-hr in the 1980’s (Sawyer and Johnson, 1995).
In order to bracket the exposure of the railroad workers to diesel exhaust a variety of patterns of
exposure are considered. The patterns are characterized by two components: a) the extent of change
from 1959 to 1980 in diesel exhaust exposure, expressed as a ratio, and b) the average exposure
concentration for the workers on trains measured in the Woskie et al. (1988a) study (i.e., the baseline).
The alternate ratios are as follows: a) a ratio of 1 suggested and used in Crump et al. (1991) as more
realistic than the Garshick et al. (1987a, 1988) assumption of constant concentration from 1959-1980
and none before that; b) a ratio of 2 suggested by K. Hammond to allow for a modest peak in 1959; c)
a ratio of 3 allowing for more peak, a scaled down version of the exposure factor of 10 that Woskie et
al. (1988b) reported for exposure concentration of shopworkers to nitrogen dioxide in enclosures
including engine test sheds; and d) a ratio of 10, peak of the magnitude of values for the engine test
sheds. The alternate baselines of exposure concentrations are as follows: 1) 40 µg/m 3 , obtained by
subtracting the background measurement of the unexposed workers from the measurement of the train
workers, rounded down; 2) 50 µg/m 3 , which also subtracted background from the train worker
measurements but rounded up to allow somewhat for measurements of workers on trains not having as
much exposure to non-diesel exhaust background particulate as the clerks; and 3) 80 µg/m 3 , obtained
by assuming that the entire ETS-adjusted RSP of the train workers is diesel exhaust while the clerks are
considered unexposed to diesel exhaust (0 concentration).
The specific alternative patterns of linear decline (if any) of concentration from 1959 through 1980 are:
1) no decline, constant at the baseline values of 50, a ramp (1,50) pattern suggested and used in Crump
et al. (1991).
2) declining 3-fold from a peak of 150 to a baseline of 50, a roof (3,50) pattern, the preferred pattern in
this report;
3) declining 10-fold from a peak of 500 to a baseline of 50, a roof (10,50) pattern, suggested in
information submitted by the Engine Manufacturers Association;
4) declining, 2-fold from a peak of 80 to a baseline of 40, a roof (2,40) pattern suggested by K.
Hammond, one of the investigators in the Woskie et al. study; and
5) declining 3-fold from a peak of 240 to a baseline of 80, a roof (3,80) pattern, a variant on Pattern 3
for not subtracting background ETS-adjusted RSP in the exposed group while still maintaining
461