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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.

BY,

RED DIVER 1

Bomb Tech Extraordinaire

A comment from Steve Wood posted today on the blog states:

“The troubling part of this incident is that it was an explosion, and, at least based on press reports,there was not a fire that led to a structural failure (as in the 1996 Yamanachi Kosai fire in Japan).  Following a presentation on veterinary HBO at the UHMS meeting in Maui, a group of us were having a typical bar conversation, and during the discussion, we raised the potential risks of methane in veterinary chambers (the presenter had mentioned the use of HBO in treating GI-related issues in horses). Consider the explosive potential of a large methane release in an oxygen-pressurized (or air pressurized for that matter) chamber – the ignition energy is so low that even a very small static spark, much less than a steel-on-steel percussion spark, could trigger an explosive event.  Obviously, the jury is still out in this case, but I’d suspect that methane is a factor in this incident.”

Steve does bring up a great point with the Methane and LEL/UEL (Lower explosive levels and Upper explosive limits).  I spoke to a friend who happens to be an Arson and Explosives Investigator for the last 22 years in the L.A. County Sheriff’s Bomb Squad about this today and he agreed that even in normal non-hyperbaric conditions, the combination of 5 to 6% Methane, above 21% oxygen, a very small ignition source, and perfect conditions can cause an explosive event.  Now increase the amount of oxygen, seal it all up in a hyperbaric chamber, add double the amount of pressure and a huge spark and the result speaks for itself.  We are not saying this actually happened – but it is definitely a possibility and cannot be ruled out.

Here is some reference material on this subject: (If you are a safety director anywhere, this is great reference material to have around)

Avoiding Static Ignition Hazards in Chemical Operations

Investigation of Fire  & Explosion Accidents in the Chemical, Mining, and Fuel Industries (A manual, Kuchta)

Facts About Methane that are Important to Mine Safety

Gas Explosion Handbook (Combustion Properties of Fuel/Air mixtures)

As it stands, it may be quite some time before the details of what actually happened is released.

A couple of questions for the industry (Ron please post these questions on hyperbariclink.com as well if you do not mind)

1.  Does anyone remember exactly what happened in 2009?  The cause of the fire and death of two people?

2.  What caused the accident in 2009?  Where is the report from the investigating agency so that IDIOTS & WING-NUTS out there learn a little something before they make the same mistake again.

3.  Do animal chambers get some sort of FDA 510k pre-market notification?  The FDA regulates pet food, I could not find anything about HBO chambers for animals on their website.

4.  What are the manufacturing regulations for animal chambers?  PVHO stands for Pressure Vessel for HUMAN Occupancy, is there one for animals? PVAO? Catchy.

Looking forward to some great responses.