You are correct. The sensitivity of a sprinkler's response to thermal insult is measured by the Response Time Index (RTI) of a sprinkler. Most of the general knowledge of fire sprinklers is empirical and not the application of fundamental knowledge. I suspect that the "sensitivity" they are referring to is applied to the activation temperature and not the thermal response of the sprinkler. A reduction in temperature sensitivity would increase the response time.

The required knowledge is Heat Transfer. Thermodynamics deals with state functions. Thermodynamics is deals with state functions and does not care about what happened between a change in state. Heat transfer does care about what happens between states. The RTI is relevant to convective heat transfer and not relevant to Thermodynamics.

While we know a lot about sprinklers fundamentally, our ignorance is embodied in our empirical knowledge of sprinklers. We can apply fundamental knowledge to develop hypotheses, but more fundamental knowledge is required to increase our understanding and ability to test such hypotheses. In this context, if you are not able to scratch the glass surface with specific cleaning methods, then the rest is moot.

Ignorance tends to produce very conservative outcomes, especially in the context of prescriptive approaches. A reduction in conservatism requires additional reliable knowledge. "Don't touch the sprinkler because bad things can happen."

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