Automatic fire sprinkler systems are becoming more common in buildings around the world as they are recognized for their ability to protect lives and property from fire. To do their job effectively, fire sprinklers are engineered to be sensitive to heat, so that the sprinklers closest to the fire open quickly to distribute water, extinguishing or controlling the fire while it is still small.  But for these systems to be truly successful, it is also important that sprinklers NOT activate in the ABSENCE of a fire. For this reason system installers and users of sprinklered buildings must be careful to prevent excess heat from non-fire sources from accidentally activating sprinklers, including heat sources that have arrived on the scene fairly recently.

When a sprinkler system is originally designed and installed, building regulations require that potential sources of heat be taken into consideration. Prior to installation, sprinklers are required to be stored in a cool, dry place.  Direct exposure to sunlight and close proximity to heat sources must be avoided. While “ordinary” temperature rated sprinklers are typically installed in areas where ambient room ceiling temperatures are not expected to exceed 38oC (100oF), higher temperature rated sprinklers are available and are required to be used in areas where temperatures are likely to exceed this threshold.  Such spaces typically include areas near unit heaters, under skylights, in unventilated attics, and near heat-producing appliances and fixtures.

Although ordinary temperature rated sprinklers are designed to operate only when they reach temperatures between 57°C to 74°C (135°F to 165°F), repeated or long-term exposure to temperatures above 38oC (100oF ) can weaken the sprinkler’s thermal operating element.  While a weakened sprinkler may not fail immediately, it could potentially operate at an undetermined point in the future in the absence of a fire. 

Installing contractors should strongly consider providing specific direction to builders, within the contract documents, to avoid exposing sprinklers to excessive heat inadvertently during the completion of construction once sprinklers are installed.

During the use of a building, if it is recognized that unusual heat is to be present in an area protected with fire sprinklers, a qualified contractor or engineer should be asked to evaluate if ordinary rated sprinklers should be temporarily or permanently replaced with higher temperature rated sprinklers.

Here are some examples of potential problem areas involving excessive temperatures not related to the original building design, some of which are new:

Construction or Alteration-Related Heating

In some climates heaters are placed in areas where sprinklers are already installed to help dry plaster or paint more quickly, easily raising ceiling temperatures above 38oC (100oF ).

“Hot Yoga” Studios

Heating yoga studios to temperatures of between 32 to 47°C(90 to 117°F) has become a huge craze in many parts of the world.  Most classes reportedly aim for 37 to 41°C(98 to 105°F) to maximize the impact of the workout.

Bed Bug Remediation

While bed bugs were almost eradicated years ago, the surge in global travel and other factors have contributed to regular infestations. Room heating has become a popular treatment method and entails raising room temperatures to levels that are lethal for bed bugs in all areas the bugs can get to, including cracks, crevices, inside walls, etc. methodThe U.S. Environmental Protection Agency reports that bed bugs die when their body temperatures reach 45°C (113°F), but room treatments generally range from 47 to 50°C(117 to 122°F).

Ventless Clothes Dryers

 While ventless clothes dryers have been used in Europe for many years, they are fairly new to the North American market, where vented clothes dryers have been the norm. More energy efficient and more expensive than vented dryers, they generally incorporate condensers in a “two-loop” system to first heat some incoming air, allowing it to absorb moisture from the damp clothes, then continually condense the heated moist air to release the water before recirculating the resulting dry air within the clothes dryer. Unlike vented dryers, where moist heated air is exhausted to the building exterior, these devices capture the water to a drain or pan, while the heat from the condensing cycle is exhausted into the immediate area. Ventless dryers are so unusual in North America that the NFPA sprinkler installation standards don’t yet include them in the lists of heat sources (fireplaces, ranges, heat ducts, water heaters, skylights, etc.) for which higher temperature classifications of sprinklers must be used.

The condensers in combination machines that both wash and dry the clothes are generally water-cooled, such that quantities of cold water are used to condense the moisture evaporated from the clothes during the drying cycle, and pumped away through the drain line. But the standalone dryer units are air-cooled, using the ambient air as a heat sink. While this heat can be dissipated in a large laundry room, it can be expected to raise the temperatures within a laundry closet to levels unacceptable for ordinary temperature rated sprinklers. All makes of standalone ventless dryers are reportedly of this type.

In all of the above situations, the replacement of ordinary temperature rated sprinklers with higher temperature rated sprinklers can help avoid the possibility of an unwanted sprinkler discharge. With proactive communication, and adherence to code requirements and common sense best practices, installers, builders, and property owners can have a greater sense of confidence that their automatic fire sprinkler systems will perform as intended.