About 25 million Model GB sprinklers are installed worldwide. It is not known how many of Central's Model GB sprinkler heads may be leaking, and neither Underwriters Laboratories nor FM Global has received any report of Model GB sprinklers failing to activate in a fire. It is too early to consider any recall or replacement of the sprinkler, said Brad McGee, senior vice president of Tyco International, which acquired Central last year. The company advises inspecting the sprinkler heads for signs of leaks. Glass-bulb sprinklers contain alcohol or another liquid in a bulb mounted on the sprinkler head.
Heat rising from a fire expands the liquid, causing the glass to shatter.
That releases the sprinkler's plug and allows water onto the fire. An O-ring seal keeps the plug from leaking. Underwriters Laboratories observed crystallized deposits or corrosion around the rubber seal, which indicated leaking water. The sprinkler model recently was redesigned with a metal seal. About 15 percent of the 135 sample sprinkler heads tested did not operate at a water pressure of five pounds per square inch, the pressure at which sprinklers are required to operate in order to earn a Underwriters Laboratories listing.