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Electric Outlet Explosion

Physical Chemistry




Areas of Expertise

Michael Fox, PhD.


Electric Outlet Explosion Investigation

Two workers investigated an irrigation timer connected to an electric outlet in a pool equipment shed at a residence on Maui. Allegedly, when one of the workers jiggled the transformer that was plugged into an electric outlet, the electric outlet exploded and sent a fragment of plastic into the eye of one of the workers. The injured worker sued the homeowner. A photo of the pool shed from the outside is shown below.

photo of the pool shed from the outside

A photo of the electric outlet that allegedly exploded is seen in the photo below. This photo was taken within 3.5 months of the incident and it was claimed that the outlet had been replaced after the incident, but there was no record of any replacement. The homeowner had been on the mainland for an extended period of time during the incident and afterwards. It did not go without notice that the outlet appeared to be older than 3.5 months.

photo of the electric outlet

The plaintiff's theory was that there was a hydrogen explosion inside the electric outlet. The plaintiff's expert opined two possible mechanisms for the hydrogen explosion. The first was that pool chemicals generated hydrogen chloride (HCl) that entered the electric box where it reacted with metal to form hydrogen gas (H2). The second was that water (humidity) entered the electric box and hydrogen was formed by electrolysis. The plaintiff's expert was a professor of chemistry for many years, but had no fire and explosion experience. For example, he did not know the meaning of LEL (lower explosive limit) and did not know that the LEL for hydrogen gas is 4% by volume (40,000 ppm).

Dr. Fox evaluated the two proposed hypotheses of the plaintiff's expert and concluded that neither could happen by any natural process.

First of all, however the humidity or HCl diffused into the box, any H2 formed would diffuse out 3-4X faster than H2O or HCl could diffuse into the box. In other words, there was no mechanism by which H2 could accumulate to its LEL of 40,000 PPM by volume. Measurements of HCl in the pool shed, before opening the shed, did not detect any HCl above 10 PPM, the detection limit. If 10 PPM HCl were converted to H2 gas by corrosion, the highest H2 concentration possible would have been 5 PPM H2.

2HCl + M => H2 + MCl2

If the HCl concentration was anywhere near the 80,000 PPM needed for create the 40,000 PPM of H2 needed for an explosion, the workers would have been driven away by the HCl fumes long before they could get near the electric outlet.

Even the plaintiff's expert acknowledged that in order to have electrolysis of water, there needed to be enough liquid water to make a complete electric circuit between the two electric wires inside the box. That amount of water, over 100 ml, could never accumulate by any natural process (humidity). Furthermore, the weather reports indicated that the dew point had not been reached for longer than a week prior to the incident. If the dew point is not reached, liquid water cannot accumulate via humidity. There were no reports of any water leaks inside the pool shed.

Not withstanding that a hydrogen explosion is simply impossible by any natural means, another issue was whether or not the homeowner could have foreseen a hydrogen explosion. It took the jury 45 minutes to decide in favor of the homeowner.

Dr. Fox is a fire expert, explosion expert and chemical expert with extensive experience in OSHA, EPA, and DOT chemical regulations and chemical safety.