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On August 6th, 2008, at approximately 2300 hrs, Tacoma firefighters responded to a presumed pipeline fire at the âTâ street gulch in northern Tacoma. As the response evolved, it was hypothesized that the actual source of the fire was a section of burning storm water drainpipe that drained into the gulch.
Drain pipe in this area is composed of a black, high density polyethylene plastic. An unknown event triggered the ignition of the drain pipe, which in the process melted and released gaseous byproducts. The drain pipe eventually collapsed, extinguishing the fire.
On subsequent days, as workers approached the site to begin repairs, high vapor concentrations were noted. On August 11th, 2008, the assistance of the USEPA was requested in order to establish that the pipeline could be safely accessed and repairs begun.
A small opening (approx. 100 cm2) into the collapsed drain compartment was available for monitoring purposes. Inside the opening, measurements were made of volatile organic hydrocarbons, flammable atmospheres, carbon monoxide, hydrogen sulfide, hydrogen cyanide, and chlorine gas concentrations.
The following measurements were noteworthy:
volatile hydrocarbons of 19 -35 ppm were noted
carbon monoxide 5ppm
hydrogen sulfide, hydrogen cyanide, and chlorine concentrations were below limits of detection and worker threshold values
Of special note, formaldehyde concentrations in the drain were .37 ppm as measured using a Draeger Chip Measurement System. This value is approximately half of the OSHA TWA for formaldehyde.
Four soil samples were taken, and are currently being analyzed for NW-TPH Dx, NW-TPH Gx and HCID measurement. These results should become available tomorrow.
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