Chemical Reaction

US building codes have emphasized flame spread and smoke generation. On the surface, this seems to adequately address fire safety. However, in the European Union (EU), codes also address toxic gases that can kill and incapacitate building occupants before they can safely exit a burning structure.

Today’s workplace is a canned environment. Most new high-rise buildings, especially those more than five stories, have sealed windows, part of a sophisticated air quality system intended to make occupants more comfortable and productive. If there is a fire, the smoke detectors should activate the air system dampers to keep the smoke from spreading. But, what about the deadly gases that are, most often, clear and odorless? Those threats are not recognized or controlled by smoke detectors and dampers.

In a typical office building, there are carpets, desks, furniture, paper and a host of modern plastic materials that are flammable and could generate toxic gases. However since they all lie below the drop ceiling, the office sprinkler system would douse flames before dangerous heat levels are reached. Above the drop ceiling, there is a return air plenum space. The ducted cool or heated air is vented into the space below, and the return-air flows back through the open area above the ceiling. All building materials used in the return-air plenum space are supposed to be labeled limited combustible, except communications cabling, which is plenum rated (CMP).

In case of fire …

During a fire, occupants of the structure should try to exit immediately. However, they may be blinded and choking from either heavy smoke or acids from invisible gases. Typically, fire injuries and death occur as a result of a two-stage process. The first stage is incapacitation, which results from exposure to fire effluent, consisting of smoke and a range of toxic products. This is followed by the second stage of death resulting from continued exposure to heat and toxic gases, with carbon monoxide particularly being an ultimate cause of death.

For many years, U.S. experts have acknowledged the importance of reduced flame spread and low smoke generation. The cables located in the plenum space (usually above the ceiling) are potential concealed highways for a fire to spread. Reduced flame spread is an important part of the safety formula. The low smoke generation property of the cable is designed to inhibit the obscuration factor associated with thick smoke. We need to see the exit signs and the pathways to safety. Smoke also has a choking effect when inhaled, which is one more reason to limit the smoke. Both flame spread and smoke are part of the testing criteria (UL910/NFPA 262 for CMP) for communications cables for use in return air plenum space.

Since 1975, the communications industry has installed nearly 9 million miles of communications cable in the workplace. Most of the cable is CMP, which has never been tested by code-making organizations for toxicity in a fire. But, communications consumers aren’t likely to pull out 9 million miles of toxic cables from air systems in the workplace.

So what is the safest alternative? Toxic gas sensors can be added to the same system used for smoke detectors. Several manufacturers of gas sensors identify carbon monoxide and chlorine gases. In addition, a few sensors will identify toxic gases generated by fluorine materials.

Several of the world’s leading sensor manufacturers are exploring products that will identify hydrogen fluoride (HF) gases. HF is perhaps the most reactive material known to man. It can change to hydrofluoric acid on contact with moisture (even humidity) and can even eat glass. Imagine what it would do to the eyes, nose and throat of a building occupant trying to escape a fire.

Honeywell Analytics, Lincolnshire, Ill., manufactures a few products that can identify HF. Monitors, such as the company’s Vertex and CM4 models, have a central monitoring instrument that accepts inputs from a number of sensors that can be mounted on ducts. Honeywell also has single-point monitors, such as the Apex and Midas, for $1,500 or less. One of these devices mounted alongside the air return port of the HVAC air handler could cover the area of a typical office and might be just as effective as the multipoint system.

Sierra Monitor Corp., Milpitas, Calif, also makes gas sensor modules that provide continuous trouble-free monitoring of hazardous gas conditions to protect personnel and facility. The modules condition the sensor signal and provide an industry standard 4 to 20 mA output that can interface with single or multichannel controllers and distributed control systems.

Honeywell Analytics said the company would be happy to work with designers or installers on identifying the optimum solution for a given application. This is an exciting opportunity that can significantly enhance life safety and also provide a wide-open opportunity for forward-looking contractors.

BISBEE is with Communication Planning Corp., a telecom and datacom design/build firm. He provides a free monthly summary of industry news on

About the Author

Frank Bisbee

Freelance Writer
Frank Bisbee is with Communication Planning Corp., a telecom and datacom design/build firm. He provides a free monthly summary of industry news on .

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