E-diesel fire concerns still not completely 'arrested'

Diesel Fuel News, July 21, 2003 by Jack Peckham

Tests of flame-arrester devices on diesel fuel equipment tanks show that all concerns about fires and explosions from ethanol-diesel ("e-diesel") blends have yet to be resolved.

Under contract from the U.S. National Renewable Energy Laboratory (NREL), fire-technology experts at Southwest Research Institute (SwRI) found that some flame-arresters work better than others in preventing "e-diesel" flame propagation.

Wire-mesh type flame arresters installed in diesel fuel-tank fill necks or fill mouths were "insufficient for all tank and fill neck designs," the SwRI investigators found. "Coarser meshes could not stop the propagation of flames and the tighter meshes would deteriorate after being tested only a few times."

In contrast, a stamped-steel flame arrester "was found to be sufficient for all fuel tanks" except for a saddle fuel tank, they found.

"None of the flame arresters would prevent ignition from propagating from the fill port into the fuel tank while still allowing fuel flow for the saddle tank," SwRI researchers Nathan Wyandt and Marc Janssens report in their paper (see: www.nrel.gov/docs/fy03osti/34301.pdf). "It may therefore be necessary to design a fill neck as an addition to saddle fuel tanks in order to install more effective flame arresters."

Engine/vehicle manufacturers and American Petroleum Institute raised alarm bells about "e-diesel" causing possible catastrophic fires and damage to fuel systems equipment (see Diesel Fuel News 11/11/02, p9; 11/12/01, p9).

One issue: Diesel equipment operators accustomed to relatively "safe," non-explosive diesel might carelessly smoke or cause sparks while refueling equipment with "e-diesel."

Even though "e-diesel" uses a chemical additive to create a diesel-ethanol solution, "at ambient temperatures mainly ethanol resides in the headspace of e-diesel blends," the SwRI researchers note. "Therefore the flammability properties of 'e-diesel' are a significant technical challenge from a safety standpoint."

While gasoline is more explosive than diesel, in a tank its headspace is too rich to allow flame propagation downward from filler neck to fuel tank. "With ethanol fuel, however, ignition could easily propagate down a fill neck and into the fuel tank at typical ambient temperatures, causing the fuel tank to catastrophically fail," the SwRI experts found.

So, the researchers investigated a variety of wire-mesh and stamped-steel flame arresters in a range of common diesel fuel tanks, including tanks typically used for semi-trucks, pickup trucks, buses and farm equipment.

Only a 0.1-millimeter-thick stamped steel material worked to prevent flame propagation while still permitting refueling of pickup, bus and farm tanks, but it couldn't meet the refueling test on the saddle-fuel truck tank.

This stamped-steel material is ten times costlier than the wire-mesh types, estimated at about $40 per part. What's more, the SwRI researchers also "recommend the incorporation of blowout panels or other fast-acting pressure relief devices for use in 'e-diesel' fuel tanks," in case the flame-arrester fails for any reason.

So, if effective fire-prevention means replacing entire tanks rather than retrofits, then costs could skyrocket.

Even though flame-arrester-equipped tanks might offer potential for commercial development, other questions arise. Who would issue type or certification approvals for tanks equipped with such devices? Would nervous engine or equipment makers balk at "e-diesel" tank retrofits on existing vehicles/engines, or would such approvals only come for new engines/equipment? Who would ensure that retrofits are done correctly?

"That's a good question," SwRI researcher Nathan Weyandt told us. "There's no real test standard, like SAE or some other certification spec" for this unusual application.

In any case, insurance companies "would have to be very interested" in seeing some sort of type approval, he said.