RTI – Response Time Index

Depending on the fire hazard and building type, international approval regulations require fire sprinklers to have thermal sensitivity characteristics that define its ability to control or extinguish a fire. One measure of thermal sensitivity is the Response Time Index (RTI) measured under standardized test conditions, based on the response time of a sprinkler when exposed to a defined hot air stream.

RTI=(\frac {-t_ru^{1/2}} {ln [1-\triangle T_b(1+C/(u)^{1/2})/\triangle T_g]}) ·[1+C/u^{1/2}]
Release Time
Norbulb modelTime (s)(ms)1/2(fts)1/2

Response classes

RTI >80 (ms) ½

Standard Response requirements are stipulated in all applicable international approval regulations. Norbulb N5 glass bulbs are designed to meet these requirements.

RTI 50-80 (ms) ½

Special Response has been established as a classification in Europe for selected fire risks and sprinkler types in accordance with VdS 2160 and ISO 6182-1 standards. Norbulb NF5 glass bulbs are the perfect design for these sprinkler applications. They intelligently combine the standard 5mm diameter glass bulb with the patented fast filling fluid.

RTI <50 (ms) ½

Fast Response properties are a necessity for all Life Safety applications. Wherever hotels, hospitals, public buildings, office houses and private residences are subject to US ordinances, Fast Response Sprinklers approved under UL 199 QR, UL 1626 or FM Class Series 2000 test regulations are mandatory. Because of the excellent record all recognized approval authorities have added these Fast Response requirements to their standards.

The answer to this challenge are Norbulb N3 and Norbulb N2.5 series glass bulbs with specially developed and patented fast filling fluids resulting in superior performance.