Environmental and Occupational Health

Solve your monitoring needs

November 11, 2010
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In workplaces where toxic gases can exist, gas monitoring and detection equipment plays a vital role in daily operations and safety procedures. A variety of industries - including petrochemical, agricultural, construction, mining and public works - face the challenges of routinely monitoring toxic gas levels.

Toxic gases can cause exposure-related symptoms such as dizziness, drowsiness, confusion, headaches, and in severe situations, comas and death. The risks are compounded in confined workspaces such as fuel cells, fuselage, vessels, silos, culverts and vaults.

Understanding gas detection options requires an understanding of the basics of gas monitoring as well as an awareness of the technology currently on the market.
 

Gas detection basics

Gas detection and calibration equipment is generally used to measure both gases and vapors. Gases expand to take the volume and shape of their container. They have one defined state at room temperature, can be compressed and can revert to a liquid state by lowering the temperature and increasing pressure. Vapors, on the other hand, are substances that are in a gaseous and liquid equilibrium at room temperature at a given pressure. Vapors can be returned to a liquid state by lowering the temperature or increasing the pressure.

OSHA has outlined standards and protocols for atmospheric monitoring in workplaces, referred to as 29 CFR 1910.146 © C & D. These regulations require that three common hazard groups be monitored: oxygen, combustibles and toxics.

Oxygen can pose a risk when either an oxygen-enriched atmosphere or an oxygendeficient atmosphere exists. The ideal oxygen concentration is 21 percent, but a range of 19.5 to 23.5 percent is considered safe. Any atmosphere with more than 23.5 percent oxygen is considered an enriched atmosphere and presents an extreme fire hazard. An atmosphere with more than 35 percent oxygen could be combustible. If oxygen levels reach 8 percent or lower, humans can experience mental failure, difficulty breathing or death in a matter of minutes. Today’s gas monitoring instruments generally sound a warning when oxygen levels reach the minimum (19.5 percent) or maximum (23.5 percent) safe levels.

Combustibles are gases or vapors that, when combined with oxygen in the free air, are flammable or explosive. For combustibles to enflame or explode, three components must be present: a fuel source (combustible gas), oxygen (air) and an ignition source (a spark or flame). These three components are referred to as the “fire triangle.” The critical point is when the gas/air mixture falls between the lower explosive limit (LEL), the concentration below which there is not enough combustible gas to support combustion, and the upper explosive limit (UEL), the concentration above which there is not enough oxygen to support combustion.

The third hazard group is toxic gases, most commonly, carbon monoxide (CO) and hydrogen sulfide (H2S). Carbon monoxide, an odorless, colorless, tasteless gas produced by burning carbon-based fuels, inhibits the flow of oxygen through the body. Hydrogen sulfide, a colorless gas with an odor like rotten eggs, can cause loss of smell and asphyxiation. Hydrogen sulfide is heavier than air, while carbon mon- oxide is slightly lighter than air. Both gases can be highly combustible. When taking samples, consider multiple sample points to make sure the results are accurate.
 

Legal limits

OSHA has established legal exposure limits to more than 500 hazardous substances including oxygen, combustibles and toxic gases. These permissible exposure limits (PEL) are usually given as a time-weighted average (TWA), or the average exposure over a specific period of time, usually up to eight hours. This means that, for limited periods, a worker may be exposed to concentrations higher than the PEL, as long as the average concentration over eight hours remains lower. In other cases the PEL is given in short-term exposure limits (STEL), which is the average exposure over a 15- to 30-minute time period of maximum exposure during a single work shift.
 

Trends in gas detection

A wide range of gas detection monitors and calibration equipment are available today. Because gas hazards can vary extensively by industry - and because each hazardous gas has its own established exposure limits - ” it is important to work with a local distributor to identify gas detection products that would best suit an individual site application.

Modern gas detection equipment features smaller, lighter weight instrumentation and smaller sensors than traditional equipment. Newer models can feature color graphics and digital displays, more reliable power sources, built-in pumps, and motion sensors.

Many manufacturers are working toward GPS capabilities, and wireless technology is becoming more available in fixed systems. Many markets are seeing a shift from single-gas monitors to multi-gas monitors, and overall, gas detection equipment is becoming more cost-effective to own and maintain.

Most manufacturers offer technical data pertaining to gas detection equipment on their websites. Some provide online training and can customize gas detection monitors to meet specific needs. Others offer services that do not require a client to purchase traditional gas detection equipment. Some distributors offer rental equipment for short-term needs and can also provide technicians and repair services. In fact, today’s gas detection technology offers solutions to address the unique needs of almost any industry or work environment.
 

SIDEBAR: Selecting equipment

When determining the type of gas detection needed for a specific situation, consider the following:

  • Why is the measurement being made?
  • Does the situation require continuous monitoring, whether portable or fixed?
  • What detection is required - what gases are present?
  • Is record keeping preferred or required?
  • How many locations are in question?
  • Are the areas hazardous - do they require intrinsic safety considerations?

When choosing a monitor, the following features and benefits should also be considered:

  • Are replaceable batteries and sensors required?
  • Is an extended battery life required based on factors such as temperature, type of sensor and how much electronic sampling is needed?
  • Will detection take place in inert or oxygen-deficient, atmospheres? Photo ionization detectors (PID’s) and infrared (IR) sensors are the most common choices for inert atmosphere detection. PID’s measure volatile organic compounds and other gases in the atmosphere, while IR sensors detect the infrared wavelengths of toxic and combustible gases.
  • How many sensors are required for the application or situation? Instruments are available that can carry up to six sensors.
  • Is docking capability desired? Docking provides the means for calibrating on schedule, bump testing, function testing, downloading collected data, record keeping, networking, etc.
  • s on-screen graphing desired?
  • Are color displays, built-in correlation factors or configurable data logging desired?

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