Can you provide a reference to the scientific study? While not related to this topic, I would be interested in reading this paper.

I do not believe that it is the expansion of the liquid in the bulb that results in the bulb failure. If you look closely at the bulb, there is a relatively small air bubble in the liquid. The volume of this bubble is carefully calibrated to achieve the desired activation temperature. Again, fundamental knowledge applied to the glass bulb would show that the thermal expansion coefficient is significantly different for liquids than for gasses. The expansion in volume of the air bubble causes an increase in pressure in the liquid.

The pressure inside the glass bulb will be uniform. The stress in the glass will not be uniform due to concentrations of stress based on the geometry of the glass. At the ends of the glass bulb where in contact with the cap and the frame arm, there will be stress concentrations where the bulb will break first.

Again, the first test of the hypotheses would be to test whether the cleaning agents or methods will produce scratches in the surface of the glass.

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