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Explosion at a Nitrogen Trifloride Gas Manufacturing Facility

On, July 30, 2000, an explosion occurred at a specialty gas manufacturing facility in Dayton, Nevada. The plant manufactured small quantities of nitrogen trifluoride (NF3), a specialty chemical used for etching silicon wafers and for cleaning silicon production equipment in the microprocessor fabrication industry. While the building housing the process was damaged, no personnel were injured.

 

Exponent conducted an engineering investigation of the incident to determine the cause of the explosion, to understand the chemical reactions leading to the incident, and to quantify the explosive energy of the blast.

 

The incident occurred in the last stage of the manufacturing process, inside a distillation column/reboiler assembly that separates residual nitrogen (N2) and fluorine (F2) gas from condensed NF3. A process disruption occurred approximately 90 minutes before the explosion, when the plant received a liquid nitrogen delivery that was significantly colder than the nitrogen already present in the onsite tank. Liquid nitrogen was used as the heat exchange fluid inside the distillation column condenser and the influx of the colder delivery caused sufficient temperature decrease within the column condenser to liquefy fluorine.

 

Analysis revealed that the condensed fluorine reacted with the stainless steel packing material to initiate a localized exothermic event inside the column/reboiler. The hot spot spread and initiated combustion between the stainless steel packing material and the liquid NF3. The energy released by these exothermic reactions evaporated NF3 and caused a rapid increase in the temperature and pressure of the column/reboiler contents. The gaseous outflow choked at the column/reboiler outlets and the resulting pressure buildup, estimated at approximately 8000 psi, ultimately failed the reboiler. The total energy yield was low (approximately 1.5 lb-TNT) and no one was injured. However, this incident serves to highlight the care necessary in manufacturing highly reactive fluorinated gases.

 

Figure 1.  Schematic of the chemical process used to purify NF3

Figure 1. Schematic of the chemical process used to purify NF3

 

Figure 2.  Ruptured reboiler beneath the distillation column

Figure 2. Ruptured reboiler beneath the distillation column

Related Publication

Dekermenjian M, Reza A, Koonce M, Poblotzki J.  Exothermic reactions between cryogenic fluorine, nitrogen trifluoride and stainless steel. Presented at the 37th Annual Loss Prevention Symposium, AICHE Spring National Meeting, March 2003.