The cutting of glass panes requires etching that significantly reduces the thickness and allows fracturing at a lower applied force. Most likely a "scratch" on the surface would not be sufficient to reduce the area to produce a fracture at the applied force on the glass bulb.

Cyclic fatigue can also produce failure in materials at areas of localized stress. The cycle can be produced by changes in temperature that changes the applied force o the bulb. Most sprinkler bulbs are not exposed to relatively large temperature differentials. At most, 150 degrees F to 40 degrees F. The service life of a sprinkler would most likely not be capable of producing the number of cycles required for cyclic fatigue failure.

A third consideration (Mechanics of Materials) would be the hardness of the glass as compared to the hardness of the materials used in the cleaning. "Scratches" produced by a materials in contact motion with the surface of the glass bulb would have to higher on the hardness scales relative to glass. While no material used to produce such scratches is identified as part of this hypothesis, it is difficult to see how this condition would be met in the cleaning of sprinkler glass bulbs.

For these reasons, I would question the reliability of any determination that the practical cleaning of the glass bulb would reduce the sensitivity to heat of the bulb. At best, it is an untested hypothesis.

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