Nitrous oxide (N2O), a substance that is stable under normal handling and circumstances, exploded when it became overheated in a pump being operated at an Airgas facility in Florida in August 2016, reported the U.S. Chemical Safety Board (CSB). The explosion resulted in the death of the worker operating the pump, the only person at the facility at the time of the accident. The CSB found that N2O is largely unregulated under federal law requiring process safety management. CSB’s report includes several safety recommendations to Airgas and other parties in a position to promote the safe handling of the substance.
N2O is a clear, colorless, oxidizing liquefied gas that is classified by the U.S. Department of Transportation as nonflammable. However the Compressed Gas Association notes that N2O will support combustion at temperatures in excess of 650oC (1202oF). The best-known use of N2O is as an anesthetic and as an analgesic for medical and dental patients. It is also used as a food processing propellant; an auto racing engine injection; and in semiconductor manufacturing, chemical manufacturing, and analytical chemistry.
Inadequate Process Safety Management
According to the CSB, on the day of the explosion, a pump used to transfer N2O to a trailer heated the gas above its safe operating limit and triggered a violent decomposition reaction. In addition to killing the operator, the explosion scattered large metal fragments hundreds of feet.
In its final report, the CSB notes that the contributing causes of the explosion all stemmed from the lack of an effective process safety management system. For example:
- Heat from the pump was a known hazard, but Airgas did not evaluate safety design options that could have eliminated the need for the pump altogether.
- The company did not perform a management-of-change review or hazard analysis before installing the pump to identify and control hazards.
- Safeguards installed by the company, including the safety interlock to automatically shut down the pump and flame arrestors, were likely ineffective and failed to prevent the incident.
Unregulated Under RMP and PSM
The CSB notes that the major safety hazards associated with N2O manufacturing are regulated neither under EPA’s Risk Management Program (RMP) nor the Occupational Safety and Health Administration’s (OSHA) Process Safety Management (PSM) regulations, even though there have been process safety incidents such as violent decomposition of N2O and the rupture of N2O tanks that have occurred at production, storage, and distribution facilities.
CSB’s recommendations are that Airgas, the Compressed Gas Association, and two N2O pump manufacturers develop and implement a safety management system standard for N2O manufacturing, and distribute increased warnings about N2O decomposition hazards.
CSB’s final report is here.