Society of Fire Protection Engineers
New Zealand Chapter
SPRINKLER RESPONSE TIME INDICES
Chris Mak, Company Engineer, Wormald New Zealand Limited
2. RESPONSE TIME INDICES
An international working group on sprinkler and water spray product performance standards agreed tentatively on specific ranges of RTI’s and conductivity of sprinklers, to categorise them as standard, special or fast response sprinklers. Generally, fast response heads have an RTI of less than 50 m½ s½, special response heads have an RTI between 50 and 80 m½ s½, and standard response heads will have an RTI of between 80 m½ s½ and 350 m½ s½. Note that "abnormal" conductivities would affect these definitions.
3. PUBLISHED DATA
The sprinkler bulb manufacturers do publish this information in the form of a Technical Specification.
How does this effect fire engineering calculations?
As fire engineers, are concerned about the use of sprinkler RTI’s, when designing to the limit. There are a number of parameters that may be significant in delaying sprinkler detection and operation times. We also question whether it is necessary to have a maintenance contractor know what sprinkler head RTI is required, if the heads need replacing, especially as the information is not published by the sprinkler head manufacturer. How do we control long term that activated sprinklers are replaced with an equivalent RTI?
Thus, we would suggest that some conservatism is used in designing and specifying sprinkler head RTI’s. We would suggest the following figures, based on the ISO recommendations:
i) Fast Response (3mm bulb) 50 m½ s½
ii) Intermediate Response (4mm bulb) 80 m½ s½
iii) Standard Response (5mm bulb) 135 m½ s½, (8mm bulb) 250 m½ s½
This will allow any head to be replaced with any head with equivalent hydraulic characteristics, and meet the full requirements of the fire engineering design for the building.
We note that these figures are offered for discussion purposes only, and we undertake no warranty as to their suitability for use in specific fire engineering calculations.
6. OTHER ISSUES
We have taken the opportunity to discuss other issues with respect to sprinkler heads :
i) Residential Heads
We have seen residential heads specified to meet not only RTI criteria, but also a temperature rating of 57° C. The National Fire Sprinkler Association 1995 listing of residential heads lists two heads rated below 68° C, namely, GEM’s FR1 - Fusible Link Horizontal Sidewall, and Reliable F4/Res Concealed head. Both these are specialised heads, and not suitable for most installations. Residential heads have been designed to operate quickly, and control a fire prior to any life threatening situation.
Thus, we question whether it is really necessary to specify sprinkler design parameters? If so, we would ask that the industry norms are specified, viz, either 68° C (bulb) or 71° C (fusible element).
ii) Quick Response vrs Fast Response
We note that there is some confusion with respect to the definition of quick response and fast response. We offer the following interpretation.
A fast response head is just that. A head with a fast response element. A quick response head also considers the coverage of the head, which is fire tested. Thus, a quick response head is tested to operate within a set time, in a set room geometry. To illustrate this, an extended coverage ordinary hazard head uses fast response elements, with an extended coverage deflector, which has been demonstrated to equal a standard sprinkler head, via fire tests. The head is not a quick response, as it is listed for a maximum spacing of 6.1m. The fast response element with extended spacing is considered equal to a standard response element, with conventional spacing.