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Every reader of this column is intimately familiar with cow tipping and, undoubtedly, spontaneously combusting bovine mammals. For the following twist on that same theme, I need to thank Lt. Phil Lyons, Fire Prevention Officer and Investigator with the Tukwila Fire Department, for sharing an article with me on the killer in our kitchens disguised as a dishwasher. Yes, a dishwasher - a potentially murderous dishwasher. It seems a U.S. Navy housing inspector was doing a routine bi-monthly check on vacant buildings at his base. His normal routine was to flush the toilet and run the dishwasher while he proceeded with the rest of the inspection.

But on this particular day, three minutes after he started the dishwasher, it exploded. The appliance was driven across the kitchen, damaging the plumbing, cabinets and wall; plus it blew apart the rear door of the building.

Investigators initially surmised water in the "P" trap had evaporated, allowing sewage gas to enter the dishwasher and explode. Methane gas produced by decaying vegetable matter has been known to combust on occasion when it leaks from sewage systems. Alas, methane was not the problem they soon discovered.

According to the article, one of the investigators found a little-read paragraph inside the owner's manual about hydrogen-gas production in hot-water systems.

It seems hydrogen gas can, under certain conditions, build to unsafe levels in systems that have not run for two weeks or more.

The investigating engineers explained that because of the way the hot-water-heater tank was constructed, there was no way to stop the production of hydrogen gas.

Hydrogen isn't water soluble, and it remained in the plumbing system as a gas under pressure.

The gas normally migrates to the top of the plumbing system, where it is drawn little by little from faucets, thus becoming part of the greater atmosphere.

In homes where the hot water is not drawn regularly, and a lower-level faucet or appliance is used first, the gas is forced out at that level.

The theory behind this explosion was that the hydrogen was ignited by the timer or relay switch inside the dishwasher because hydrogen gas has an extremely wide range of flammability and will explode at just about any mixture, if a source of ignition is provided.

This was the first exploding dishwasher on record. People in the water-heating industry say that a washing machine is known to have exploded in the 1960s.

And several small fires at faucets have occurred when hydrogen gas was relieved next to a burning cigarette.

Safety investigators recommend that occupants who have been away from a building for an extended period of time first run their hot-water faucets to relieve gas. And they should not smoke while doing so.

The article did not say whether turning off a hot-water tank that isn't going to be used for several weeks eliminates the problem.

Is this heat-related, or a chemical reaction that happens whether the water is hot or cold? Readers, share your knowledge, please.

Q: Why does my GFCI breaker have test and reset buttons?

A: A large percentage of Ground Fault Circuit Interrupters do not function as they should. They are designed to be tested regularly by pushing the "test" button to cut power, and then restoring power by pushing the "set" button.

The American Society of Home Inspectors and the manufacturer Leviton recently performed a nationwide study and found 15-19 percent of the breakers do not function, depending on type.

Areas with high numbers of lightning strikes had higher malfunction rates, as high as 58 percent in Florida. Our area had a 7 percent failure rate on receptacle-mounted units and 17 percent on circuit-breaker models (which are generally older).

Leviton is marketing a new model GFCI that cannot be reset if it fails the test phase. It has lights to indicate whether it is wired to the system improperly, a great safety stride.

Darrell Hay answers readers' questions. Call 206-464-8514 to record your question. Or e-mail dhay@seattletimes.com. Sorry, no personal replies.