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How it Works: Automatic Fume Hood Fire Suppression

Firetrace International, located in Scottsdale, Arizona, manufactures automatic fire detection and suppression systems.

by Firetrace International
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Problem: Working with volatile chemicals and hazardous materials presents serious challenges. The fumes that emanate from these substances can be dangerous to inhale and in some cases highly flammable. To prevent fumes from accumulating, work is typically done in a laboratory fume hood, which is designed to draw fresh air through the sash into the work area, past the baffles, and out to the exhaust duct.

While fume hoods are good at controlling the risk of fume inhalation, that same protective airflow also contributes to the risk of fire. Most laboratories have procedures in place to help prevent fume hood fires, however, the presence of ignition sources such as hot plates, Bunsen burners, pyrophoric materials, and the inherent volatility of the many chemicals typically found in laboratories can easily result in a fire-related incident. Should a fire start, the airflow in the hood can inhibit the ability of the lab automatic fire sprinkler to react to the fire. The delay in the detection and suppression of the fire can lead to serious losses.

To combat the threat of fire, in-cabinet fire protection has become a popular option. The most common type of protection is a self-contained sprinkler head type dispersal system that has a heat-detecting sensor mounted above the fume hood work area that activates via a heat sensitive glass bulb. While this type of system is better than nothing at all, the airflow pattern in a fume hood severely limits the fire-detecting ability of sprinkler head systems.

When a fire breaks out in a fume hood, the heat and flames immediately begin to follow the airflow pattern throughout the cabinet increasing the probability that the temperature required to activate the system may never reach the detection device.

Solution: The key to quick and reliable effective fume hood fire-detection and suppression is actually quite simple. To be effective, the fire detecting sensor must be located directly in any path the airflow in the hood may direct the heat and flames.

Firetrace International, located in Scottsdale, Arizona, manufactures automatic fire detection and suppression systems that utilize unique, flexible, pressurized polymer detection tubing that can be routed unobtrusively behind the fume hood baffles and across the exhaust duct openings. These areas, by design, are exactly where the heat and flames from a fire travel.

The detection tubing, which is actually a very precise linear pneumatic heat sensor, is designed to burst when it detects the radiant heat of a fire. When the tubing bursts the drop in pressure opens a valve that triggers the release of a fire extinguishing agent through nozzles located in the hood. Placing the tubing directly in the path of a fire results in quick detection and suppression (more than 10 times faster than other systems) that can minimize or eliminate fire damage to the hood and smoke damage to lab equipment and instrumentation. With a Firetrace system, most fume hood fires are extinguished in 10 seconds or less.

Firetrace systems are compatible with more commercially available extinguishing agents. For fume hood applications, the company recommends multi-purpose (ABC) dry chemical fire extinguishment or carbon dioxide (CO2). Dry chemical is widely accepted as the most effective agent available for extinguishing flammable liquid fires. It is ideal for fume hood applications because it does not react negatively with most chemicals. CO2 is electrically non-conductive and effective on Class A, B and C fires. CO2 is also desirable for fume hood applications because it will not damage sensitive equipment and will suppresses a fire without leaving behind any residue.

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