Water Heaters to be Fire Resistant

June 1, 2003
BY ROBERT P. MADER Of CONTRACTORs staff BEGINNING JULY 1, all water heater manufacturers in the United States will begin manufacturing 30-, 40- and 50-gal. gas-fired atmospheric vent water heaters that are flammable vapor ignition resistant. The water heaters will be designed to meet ANSI Z21.10.1-2001, which addresses the problem of people who dont understand that its unwise to use or store gasoline



BEGINNING JULY 1, all water heater manufacturers in the United States will begin manufacturing 30-, 40- and 50-gal. gas-fired atmospheric vent water heaters that are flammable vapor ignition resistant. The water heaters will be designed to meet ANSI Z21.10.1-2001, which addresses the problem of people who don’t understand that it’s unwise to use or store gasoline next to an open flame.

The water heater industry collaborated to create the ANSI standard. All of them have selected slightly different ways to make their water heaters flammable vapor resistant, although the outcome is the same — if gasoline spills, any fire has to take place inside the combustion chamber of the water heater, not in the garage, basement or wherever the water heater is located.

"There are a lot of competitive issues arising out of this, and we’re trying to be honest about the fact that everybody’s design that’s out there we expect to work and to work well," said Jason Riopelle, product manager, A.O. Smith Water Products Co. "The whole idea is to make water heaters safe for everyone."

All the water heater manufacturers have striven to make sure that water heaters remain the same size for easy retrofits. The idiot-proofing technology will add $60 to $100 to the cost of a water heater at the wholesale level.

The ANSI standard has a rigid test protocol that includes spills of a gallon of gasoline both toward and away from a water heater. The test is conducted using both summer and winter blends of gasoline.

The water heaters use some type of arrestor plate that allows combustion air to pass through, so that flammable vapors would burn on top of the arrestor plate inside the water heater. The flame, however, would not be able to pass backward through the arrestor plate and start a fire inside the room.

The use of arrestor plates with hundreds or thousands of small holes created another problem, however — what if the holes became clogged with dirt? The water heater consortium created a lint, dust and oil test. To pass the "LDO" test, the design of the water heater had to prevent the arrestor plate from clogging and the water heater had to remain fire resistant.

All water heater manufacturers have had their units tested at the CSA testing laboratory in Cleveland. Rheem Water Heaters has gone to the expense of building a replica of the CSA testing facility at its Montgomery, Ala., plant. When CONTRACTOR toured the Rheem testing facility this past winter, the harshness of the LDO test was readily apparent. The air was thick with vegetable oil, fine dust and cotton lint, and the water heater and everything else in the room were heavily coated with the mixture. The test is far worse than anything that would be found in any utility room.

The burn test is straightforward. When gasoline is spilled, the room cannot catch fire. The test is conducted for two hours or until the level of gasoline vapors in the room falls below a predetermined level. The Rheem testing facility includes a mechanical "person" that moves back and forth to create air movement in an attempt to stir up a fire.

Water heater manufacturers have used different materials and techniques in the design of their flame arrestors. Two big what-ifs facing design engineers were what if the flame arrestor plate corrodes from flue gas condensation and what if the flame arrestor plate gets too hot from the fire and ignites gasoline vapors below it.

A.O. Smith, State and Maytag water heaters use a ceramic used for cooktops that the company found during a trip to the ISH Show in Frankfurt, Germany, Riopelle said. The ceramic won’t rust and will remain below the temperature at which the gasoline vapors will spontaneously ignite.

A temperature sensor in the thermocouple shuts off the gas valve once a fire starts.

"The whole point of the flame arrestor is to burn off the gasoline," Riopelle said. "Most times it goes poof and consumes all the oxygen in the room. We’ve had some go for an hour or so. Most times we have not had a problem with the added temperature [a gallon of gasoline contains about 400,000 Btuh] and the temperature and pressure relief valve can handle expansion of the water."

American Water Heater, which has had a flammable vapor resistant unit on the market since 1999, uses a stainless steel arrestor plate, said Tim Shellenberger, senior vice president/engineering.

Bradford White has selected a flame arrestor of 304L stainless steel that’s micro-louvered rather than having straight holes through a piece of steel, explained Mike Gordon, vice president/engineering.

"The louvers increase the velocity of the gasoline vapor and the air so they’re going forward faster than the flame can go backward," Gordon said. "The real technology is in the changes of direction that make it nearly impossible for the flame to come back."

Rheem believes that the safest approach is to close off the combustion chamber entirely. While Rheem uses an arrestor plate, it also has a spring-loaded opening for combustion air that’s held open with a fusible link, like that used in fire sprinklers, explained Jim Bienias, senior product manager/residential. When gasoline vapors are ignited in the combustion chamber, the heat melts the fusible link and the spring slams a plate shut over the combustion air opening, sealing off the combustion chamber and the fire inside.

Water heater manufacturers have different philosophies on whether a water heater that’s been subject to a gasoline fire should be repaired and reused.

When the plate slams shut underneath the combustion chamber of a Rheem water heater, that unit is done. Rheem believes that a water heater that’s been in a fire should never be reused, Bienias said. Moreover, the company fears that homeowners may try to relight a water heater during a still potentially hazardous situation.

A.O. Smith, State and Maytag water heaters can be repaired and put back into use. Because most fires last 10-15 seconds, Riopelle said, the company has tested water heaters that have experienced multiple fires that they are repairable, "although it may make more sense to replace the water heater."

The thermocouple, igniter and pilot assembly are all one unit, Riopelle explained, so removal of two screws pops the old one out and a new assembly slides in.

Bradford White has located its thermocouple wires so that they would be burned up in a fire, Gordon said. The homeowner would be compelled to call his plumber and Bradford White advocates that the water heater be replaced.

American Water Heater has a “one-shot” sensor that’s destroyed in a fire that will disable the thermocouple, Shellenberger said, so the water heater must be replaced. He strongly suggested that the cause of the fire be investigated and flammable liquids removed from the room.

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