Table 3 further reveals that gaseous PCE, the second largest VOC
peak detected, exhibited a concentration two orders of magnitude
lower than that of TCE. In addition, 3 × 10−9 moles of phosgene
was found in the exhaust gas. Using the constant pumping rate
attached to the sorption tube, the concentration of phosgene in the
gas stream immediately above the sand surface was 0.04 mg/m3,
which is an order of magnitude below the OSHA and NIOSH regulatory
limit for phosgene (0.4 mg/m3) [40]. Given the current state
of the art of smoldering chemistry, it is not possible to relate the
quantity of PCE or phosgene to the amount of TCE that was burnt.
While Table 3 presents a simplification of a complicated system
(involving volatilization and condensation as well as pyrolysis and
oxidation), since the majority of the initial TCE mass was directly
observed, it is likely a reasonable approximation for engineering
purposes.