Ignition Source
Electrostatic discharge caused by diaphragm motion

Hydrogen was stored in a plant in a 42 ½ ft diameter sphere made of 3/16 inch steel. The sphere was partitioned into two hemispheres by a neoprene diaphragm attached around the equator. Hydrogen was stored under the diaphragm, while the upper hemisphere contained air. An explosion-proof fan was situated in the upper portion of the sphere in order to provide a slight positive pressure on the top of the diaphragm.

When the plant was shut down for a local holiday, the fan on top of the hydrogen sphere was also stopped. During plant startup two days later, a violent explosion occurred in the sphere. The sphere shell was torn into many sections by the explosion, and some of the sections were propelled as far as 1,200 ft. Some of these sections struck flammable liquid storage tanks and cracked the roofs of adjacent buildings. Most of the windows in the surrounding buildings were broken by the blast wave. Fortunately, there were no serious injuries.

A loss investigation indicated that hydrogen had leaked past the diaphragm when the fan was shut down. (The diaphragm had been installed about a year before the explosion as a replacement for another leaky diaphragm.*) Ignition of the resulting hydrogen-air mixture was attributed to an electrostatic discharge caused by the motion of the diaphragm when a compressor was started downstream of the sphere. However, another possible ignition source was the 'explosion-proof' fan at the top of the sphere.

*Hydrogen leaks across the diaphragm may have been due to the hydrogen permeability of neoprene. Measurements of hydrogen and oxygen diffusion through neoprene and other synthetic rubber skins have indicated this is the primary cause of a series of hydrogen-filled balloon explosions in Germany.

Incident Date
Dec 31, 1969
  • Hydrogen Storage Equipment
  • Vessel
  • Electrical Equipment
  • Ventilation System
  • Positive Pressure Fan
Damage and Injuries
When Incident Discovered
Lessons Learned

In any event, the lesson that should be derived from this incident is the fact that the explosion could have been avoided either by using an inert gas instead of air across the diaphragm, or by monitoring the hydrogen concentration in the upper hemisphere.