In recent years, when demand is low, the City of Montreal (like many other municipalities) has reduced the pressure of drinking water at the outlet of its production plants and pumping stations. As low water demands usually occur between 22:00 and 5:00, this water pressure « manipulation » has two main objectives:
- reduce waste within the drinking water distribution system due to its poor condition; and
- reduce stress in the pipes to decrease the risk of breakage.
In addition, on October 15, 2019, the Service de sécurité incendie de Montréal (SIM) issued a notice through the Conseil St-Laurent de l’organisation de sécurité incendie (SFPE) to :
- warn designers of new sprinkler and fire line systems to include an additional safety factor of between 10 % and 20 % in their hydraulic calculations; and
- inform owners that the performance level of their existing system should be verified, considering that this pressure reduction could result in repairs to maintain the required performance level.
The City of Montreal memo also states the following:
« In this regard, the purpose of this notice is to inform building owners, as well as designers, contractors, installers, inspectors, insurers and other persons involved, of possible variations in the water supply. » Source: click here (only available in french).
It should be noted that the NFPA 13 standard has never required that automatic sprinkler systems be designed with an additional safety factor in mind based on the results of flow tests performed. It is therefore more than likely that many existing sprinkler systems in buildings built before 2019 will no longer provide the required level of performance in the event of a fire at night, when water pressure is reduced.
Figure 1 –Sprinkler activation
The SIM’s opinion also states that « it is recommended to carry out a thorough evaluation and make changes to the systems if necessary. »
Considering this recent situation caused by the municipality’s unilateral decision, we are of the opinion that any existing automatic sprinkler system should be subjected to a performance evaluation considering the additional safety factor and the lower water pressure for several hours at night.
Indeed, the performance level of many existing systems may have become inadequate during this time period, without the owners, tenants or their insurers even being aware of it. According to the guide published by FM Global (FM 2-00 « Installation Guidelines for Automatic Sprinklers »), in addition to presenting a risk to building occupants safety, the material damage ($) caused by a fire not controlled by a sprinkler system would be approximately 6 times greater than that caused by a fire in an adequately protected building.
Depending on the size of a building, its type of construction and its uses (occupancies), it is mainly the NBC that requires that it be protected by an automatic sprinkler system. In addition, depending on other characteristics and types of storage used (flammable liquids, tires, etc.), the NFC may demand automatic sprinkler protection. When required, the NBC requests (at least since its 1960 edition) that the sprinkler system be designed and installed in accordance with the requirements of NFPA 13 standard: « Installation of Sprinkler Systems. »
Figure 2 – NFPA 13 (2016)
To design such a fire protection system, it is necessary to obtain hydraulic data from the existing water system, including its static pressure, residual pressure and available flow rate at hydrants near the building’s location. To do so, a flow test is performed according to an additional standard, NFPA 291: « Recommended Practice for Fire Flow Testing and Marking of Hydrants. »
Figure 3 – Example of flow test results
The results of the tests carried out (Figure 3) and the data obtained concerning the diameter and material of the water mains allow the designer to deduce the hydraulic characteristics existing at the entrance to the building of interest.
Based on the information/tests and data obtained, the engineer can then design an automatic sprinkler system (including pipe sizing) based on the residual pressure of a sprinkler so that it always remains above the minimum value required by NFPA 13 (usually 7 psi). In the event of significant hydraulic pressure drops (i.e. high building) or the presence of a water system that is too low (i.e. residual pressure too low), the design engineer must install a fire pump to remedy this situation. The installation of an electric fire pump requires, among other things, the use of an electric generator to take over in the event of a power failure.
Figure 4 –Fire pump
In conclusion, major rehabilitation work will be required for many existing sprinklered buildings in order to make these systems compliant and efficient according to minimum requirements. For several buildings, this work will involve the addition of a fire pump and a generator. Finally, will they have enough space to install this new equipment in their existing floor areas?
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