CTA Report, Draft 1, ISP Review - US Chemical Safety and Hazard ...

have escaped through an open oven door (Section 5.1.2), or the dust cloud may have entered the oven and
ignited.
7.1.1.3 Other Possible Ignition Sources
CSB considered other potential sources of ignition at the point of origin, as noted below, but concluded
that they were unlikely:
• Electrical equipment: Several electrical boxes containing switches and relays were located
in the area of origin and might have produced electrical sparks. The boxes were not dust-
tight, and such sparks would have been capable of igniting a combustible dust cloud. CSB
contractors examined the electrical boxes and concluded that—though they were fire-
damaged—there were no indications that the spark-producing electrical equipment inside
provided an ignition source (Appendix C).
• Lube oil system: The lube oil system and pump for the oven flights were also examined. The
piping for the high-temperature oil had no moving parts and was found to be free of leaks.
The oil pump was pneumatically operated.
• Static electricity: CSB also eliminated static electricity as an ignition source. Interviews
with line crews revealed that electrostatic discharges occurred frequently when the mat-
former was cleaned of phenolic resin. However, no one interviewed could recall an instance
when the phenolic resin ignited. Tests conducted by a CSB contractor confirmed that the
static energy in a propagating brush discharge 17 (PBD) was incapable of igniting the resin
because it did not produce enough energy (Appendix B).
17 PBDs are lightning-like electrostatic discharges. They are the most energetic of all types of electrostatic
discharges, with spark energies approaching 1 joule.
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