By BOBBY SHEIKHAN
The smoldering fumes of a recently doused fire can be filled with dangerous and toxic gases and vapors that threaten the life and health of firefighters involved in the fire overhaul operations. These threats come from the synergistic effects of chemicals such as carbon monoxide (CO) and hydrogen cyanide (HCN), which can work together to effectively shut down a person’s respiration. Direct exposure to these dangerous aerosols and particles during fire overhaul present a real risk for immediate harm or acute and chronic health problems, including heart failure and cancer.
To help protect firefighters, many fire departments are now deploying wireless gas detection systems and personal monitors once a fire has been extinguished. These systems give commanders greater visibility and control during cleanup operations and help ensure firefighters’ safety-i.e., how long to wear their air and whether it’s safe to take off their air.
Fire overhaul includes searching for possible sources of reignition and investigating the fire’s origin. The process includes sifting through smoldering ashes and partially burnt materials where poisonous gases such as CO are formed because of incomplete gas combustion. CO and HCN are just two of the potentially toxic vapors frequently found during fire overhaul operations; other chemicals and compounds include sulfur dioxide, nitrogen oxides, formaldehyde, benzene, and phosgene.
HCN is created when materials such as laminates, synthetics, foams, plastics, and wood burn. Many of these materials are found in furniture and upholstery in homes and offices; as a result, the smoke of a typical residential or office fire today is more toxic than ever.
HCN and CO-the “toxic twins”-are still present during a fire overhaul, and each can have devastating short-term and long-term health effects if inhaled. Even though there’s still a clear danger, many firefighters remove their self-contained breathing apparatus (SCBA) during overhaul operations. One reason for this is that many firefighters believe that conditions during overhaul are safer than during the actual fire. Another reason is that their SCBA gear is bulky and uncomfortable. Whatever the reason, it’s not a good idea.
HCN and CO are invisible gases that cannot be detected by the color or the amount of smoke emitted by a fire; they can only be detected by metering and monitoring. Exposure to large amounts of cyanide can cause convulsions, unconsciousness, or death. When inhaled, CO can cause tissue hypoxia, which prevents the blood from carrying sufficient oxygen and can cause dizziness; nausea; headache; and, at higher concentrations, convulsions, tachycardia, and death. When inhaled together, the toxic twins can have a synergistic effect, experts say, causing even more harm.
Figure 1 lists the HCN exposure levels deemed safe by various government agencies. Occupational Safety and Health Administration’s (OSHA’s) permissible exposure limit is 10 parts per million (ppm). At 50 ppm, HCN is considered immediately dangerous to life or health. At 3,000 ppm, HCN is rapidly fatal.
| Figure 1. Hydrogen Cyanide Exposure Levels |
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Many of the toxic gases found during a fire overhaul can only be detected with gas detection instruments. Not only are today’s gas detectors more effective than ever, they can now be connected wirelessly to create a system that makes fire overhaul much safer. A typical configuration might include the following:
- One or more area monitors;
- Personal protective equipment-clipped or handheld personal monitors; and
- Real-time monitoring and control software platform to a command center.
Personal monitors are available that can detect volatile organic compounds, toxic gases and oxygen, and combustible gases and vapors. These personal monitors can also be wirelessly connected to a monitoring network and the readings recorded to give a continuous log of time-based exposure levels. This log can then be used to verify that OSHA exposure levels for responder (or worker) safety are not exceeded.
Tying the system together is the real-time monitoring and control software platform. This platform collects data from each instrument and provides a comprehensive real-time display of gas and radiation data at any time and from any location. These data give commanders a full picture of the threats at the overhaul site and allow them to determine whether it is safe for firefighters on scene to remove their SCBA face masks and to direct firefighters to potential hotspots.
Wireless area monitoring is an effective way to have a command presence at an overhaul location. Monitors can be quickly deployed and can begin sending real-time data in minutes to a portable computer or ruggedized mini-controller. It’s a powerful tool that gives commanders vital information and helps keep firefighters safe.
BOBBY SHEIKHAN is director of product management for RAE Systems. He has provided training in air monitoring and emergency response planning for a wide range of industries. Sheikhan has a degree in electrical engineering from San Jose (CA) State University and has written articles for leading oil and gas, defense, industrial hygiene, and environmental magazines.
