A Bomb Technicians View: Possible Methane Contribution to Hyperbaric Explosion

Below is an excerpt from a highly skilled and FBI trained bomb technician & Instructor who has been investigating fires and explosions for 22 years.  Thank you very much RED DIVER1 for the quick response.

FROM RED DIVER 1 Depending on the volume and pressure of each gas present at the time of the explosion, it MAYBE possible that a spark could produce an ignition of the gases to sustain a rapid deflagration or explosion causing the chamber to rupture as the direct result of gas overpressure.

Several factors must be present to support this theory. First off, the Lower Explosive Limit or LEL must be known. Wikipedia defines the LEL as the lowest concentration (percentage) of a gas or a vapor in air capable of producing a flash of fire in presence of an ignition source (arc, flame, heat). At a concentration in air below the LEL there is not enough fuel to continue an explosion. Concentrations lower than the LEL are “too lean” to explode but may still deflagrate (burn or rapidly combust).

The Upper Explosive Limit or UEL is the highest concentration or percentage of a gas or a vapor in air capable of producing a open flash of fire in the presence of an ignition source. In this case the possibility of a spark resulting from a metal horse coming into contact with another metal surface inside the chamber, could be sufficient to cause a rapid deflagration. The resulting gas overpressure would cause the chamber to violently rupture causing heat, fragmentation and a blast pressure wave in the immediate area.

Oxygen enriched atmospheres lower the LEL and increase the UEL. An atmosphere devoid of an oxidizer is neither flammable or explosive regardless of the fuel gas concentration. Increasing the fraction of inert gases in an air mixture raises the LEL and decreases the UEL (keep in mind the fire triangle).

Methane gas has a LEL of 4.4% (at 138 degrees C) by volume, meaning 4.4% of the total volume of the air consists of methane. At 20 degrees C the LEL is 5.1 % by volume. If the atmosphere has less than 5.1% methane, an explosion cannot occur even if a source of ignition is present. When methane (CH4) concentration reaches 5.1% an explosion can occur if there is an ignition source. LEL concentrations vary greatly between combustible gases.

To prove this theory, the volume, temperatures and partial pressures of the affected gases would have to be known values to identify the upper and lower flammability/explosive limits.

In summation, it would be possible for a rapid deflagration or explosion to occur if the explosive limits are within range.



Bomb Tech Extraordinaire


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