Certain brands of water heaters set in fireplaces may pose an explosion hazard, the U.S. Consumer Product Safety Commission warned yesterday.

Compliance officer Linda Glatz said that failures of units sold under the brand names Hydrohearth, Hydroplace and Aqua Grate were believed to have caused at least eight explosions since 1977, resulting in one death and five serious injuries.

About 10,000 of those brands were made by Ridgeway Steel Fabricators Inc. of Ridgeway, Pa., and Shark Manufacturing Corp. of Greenlawn, N.Y., and distributed nationwide since the mid-1970s, Glatz said. Both companies now are out of business.

The CPSC warning does not cover fireplace-powered water heaters made by companies other than Ridgeway or Shark, Glatz said, because the agency has had no reports of those other heaters exploding and causing injuries.

Hydrohearth, Hydroplace and Aqua Grate units, which were sold at prices ranging from $200 up, are made of tubular steel or steel plate and resemble a fireplace grate or liner.

Plumbing connects the unit to the hot-water heating system of the home. When there is a fire in the fireplace, furnace heat is either supplemented or replaced entirely by heat generated through the fireplace.

Consumers who have one of the three units should have the installation checked by a qualified licensed plumber who has specific knowledge of boilers, Glatz said.