8.0 KEY FINDINGS
1. DuPont PHAs made the incorrect assumption that VF in the Tedlar process could not
reach flammable levels in the slurry tanks.
2. DuPont restarted the unit after incorrectly concluding that the defective seal loop did
not increase the risk of VF vapor transfer into tank 2. Flammable VF vapor flowed
directly from the flash tank into tank 2.
3. DuPont did not properly isolate and lockout tank 1 from in-service tanks 2 and 3 prior
to authorizing hot work on tank 1. Consequently, flammable VF vapor passed directly
from tank 2 into tank 1 through the overflow line and accumulated to a concentration
above the lower explosive limit.
4. The DuPont hot work permit procedure did not require testing the atmosphere inside
tank 1 for flammable vapor even though the work required welding directly to the tank
top.
5. The individuals who signed off on the hot work permit were not knowledgeable in the
operations and hazards of the Tedlar process.
6. The repair work created multiple ignition sources. Welding directly to the tank top
increased the metal temperature inside the tank significantly above the VF vapor autoignition
temperature. Welding and grinding generated hot sparks, which likely ignited the
flammable vapor.
7. OSHA’s hot work standard does not specifically require gas monitoring inside containers
intended for hot work even though it is recommended by industry safe practice
guidelines.