Fire Safety: Something's in the air

April 30, 2002
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In firefighting situations where hazardous substances may be present, effective detection devices could be considered a firefighter's best friend. Emergency response crews face two basic challenges when entering dangerous environments:

  • Is the air acceptable for normal, unprotected breathing? and
  • Does a potential explosive hazard exist?

Fortunately, a wide variety of gas detection equipment is available for fire service workers. Today's technology can meet almost any detection need, from simple, single toxic or combustible gas detectors to portable analytical laboratories.

However, one flexible, economical product is generally the best choice for both daily use and emergencies. The portable multigas detector is a single unit that can sense several gases at the same time - and a tool that no firefighting crew should be without.

Four types

Portable multigas detectors come in many styles and configurations. In most cases, they can simultaneously detect two to five gases and alert the user when the gas exposure level becomes a concern.

These detectors consist of multiple sensors in a single case. Instrument electronics convert the sensor output into a numerical display indicating the level of gas exposure. There are four basic types of portable gas sensors: catalytic, electrochemical, infrared and photoionization. These four sensors operate in different ways, enabling each to detect certain gases.

1) Catalytic - The two most common types of sensors are catalytic and electrochemical. Catalytic combustible gas sensors can detect a wide variety of potentially flammable gases, from natural gas leaks to gasoline spills.

2) Electrochemical - Electrochemical sensors are used to monitor a variety of toxic gases, as well as oxygen levels, to ensure that the atmosphere is not harmful to workers and that they can sustain normal breathing. The two toxic gases most commonly encountered by fire service workers are carbon monoxide (CO) from furnace leaks or car exhaust, and hydrogen sulfide (H2S) from sewer gas.

3) Infrared - Infrared and photoionization sensors are designed to detect either special gases or very low levels of gas that cannot be detected by catalytic or electrochemical technologies. Infrared (IR) sensors measure the amount of light absorbed by a gas to determine its concentration. This is the best portable gas detection method available for monitoring carbon dioxide (CO2), a common byproduct of fermentation processes such as brewing.

4) Photoionization - Photoionization (PID) sensors are used to detect volatile organic compounds (VOCs). This class of typically industrial compounds (which includes toluene and isobutylene) is sometimes present during emergency spill response actions. VOCs can be toxic at relatively low concentrations over the long term, and this has caused significant concerns in industries where worker exposure must be limited.

Portability is key

Though the sensor is the heart of the gas detector, the instrument's portability and operation should be evaluated. Portable multigas detectors range from small handheld instruments to larger units that may be placed on the ground. Since emergency response teams generally carry a large quantity of gear, smaller instruments are most practical.

First and foremost, an instrument must be able to rapidly assess gas readings in emergency situations. It should have such physical features as an easily seen display and alarm lights. In addition, it should be simple to operate and maintain. Even the smallest instruments employ sophisticated software. Before purchasing a unit, be sure to perform a trial-run and familiarize yourself with its operation.

Be prepared

Multigas detectors are used in a variety of applications in the fire service, including:

  • Confined space entry - While mainly industrial in nature, a confined space is usually defined as any enclosed area not typically meant for human habitation. Hazards include oxygen deficiency, toxic gases and combustible gases. A multigas detector can provide the appropriate measures to help ensure the confined space atmosphere is safe before your team enters and while working in the area.

  • Home calls - With the advent of carbon monoxide monitoring in the home, the number of calls to fire departments regarding home CO alarms has risen dramatically. Firefighters need to be prepared to verify the complaint upon arrival and determine if the premises are safe for habitation. They are also typically called upon to help locate the source of the gas.

    A multigas detector can help determine if the premises are safe. In addition, they often provide the leak detection necessary to locate the source of the problem. Workers may also be called in for natural gas leaks or "bad smells." Having the capability to measure several gases at once becomes a distinct advantage in these situations.

  • Overhaul - When entering damaged structures to perform overhaul operations, conditions are often uncertain. A gas detector can alert workers when it is necessary to use supplementary breathing equipment.

    Meeting the need

    From standard catalytic and electrochemical sensors to advanced IR and PID sensors, multigas detectors are well suited to meet the needs of emergency response personnel. They detect a wide variety of gases and vapors that threaten the safety of response teams.

    A standard four-gas unit with combustible, oxygen, carbon monoxide and hydrogen sulfide sensors is generally adequate for most needs. These devices can help ensure that everyone goes home safely at the end of their shift. Gas detection is fundamental to emergency response.

    SIDEBAR: Calibration - Make it a habit

    Sensor maintenance is a necessary part of proper gas detection. While most digital instruments are equipped with electronic self-diagnostics, sensors must still be checked directly.

    It is usually obvious when an oxygen sensor is inoperative since it should read near 20.8 percent under normal circumstances. If it's malfunctioning, it will likely be unable to read properly in clean ambient air.

    Other sensors, however, typically have no output - the instrument display will read "zero." To verify proper operation, you should institute a program in which each gas sensor is exposed to a known level of gas before each day's use. Without this calibration check, you could falsely assume the atmosphere is safe when it actually contains deadly gases. You don't have to fully readjust your instruments each day, but you must be certain they are operating within the manufacturer's specified limits.

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