Employee #1 and several coworkers were working at a
 chemical plant that deals with nitric oxide. On the day of the 
accident, a major leak occurred in a stainless steel distillation 
column. The nitric oxide leaked into the facilities surrounding vacuum 
jacket and into the atmosphere through a pump, which controls a high 
quality vacuum inside the jacket to minimize transmission of heat toward
 the cryogenic distillation columns. A brown cloud quickly formed and 
the temperature and the pressure inside the distillation column and its 
surrounding vacuum jacket began to rise. The leak was detected and the 
vacuum pump was turned off to halt the leakage of nitric oxide into the 
atmosphere, allowing the pressure inside the column and vacuum jacket to
 stabilize around 130 psi. Although stabilized, the pressure was far 
above the normal pressure of less than or equal to atmospheric pressure 
(14.7 psi). Approximately 3 hours later, an explosion occurred. The 
operation and process were destroyed, and debris flew through the plant.
 Employee #1 suffered lacerations due to flying glass and was treated at
 a local hospital, where he received stitches and then released. A 
detailed investigation determined that the cause of the explosion was 
most likely due to something inside the vacuum jacket initiated the 
dissociation of nitric oxide, a reaction that is very rapid, exothermic,
 and self-propagating once started. 
Source:OSHA.gov