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In general, glass bulbs are more fragile that the eutectic links. Physical damage to the surface of the bulb can produce fatigue failures over time. Impact from cleaning equipment is one means to potentially damage the glass bulb.

I investigated a sprinkler activation for a deflector that was too close to a steel bar joist. During an earthquake, the sprinkler defector came in contact with the bar joist repeatedly. The most reliable determination was that the impact imparted stress cracks in the surface of the bulb and it failed over time (years).

A good example of this was glass bulb sprinkler activations in the absence of a fire. The subsequent investigation showed that sprinkler installers were using 5 gallon buckets filled with uninstalled and unprotected glass bulb sprinklers to transport the sprinklers to their ultimate elevated position.The movement allowed impact between sprinkler heads that caused physical damage to the glass bulbs resulting in subsequent "false" activations.

Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
8940 Old Annapolis Road, Suite L
Columbia, MD 21045
(410) 884-3266
(410) 884-3267 (fax)
www.csefire.com