Industrial Gas Detection
Accurate gas monitoring, detection, and analysis equipment is crucial for protecting people and safeguarding the environments where they live and work. CoGDEM plays an important part in ensuring that standards are maintained for both products and workers in areas where hazardous gases may occur. CoGDEM assists in preparing standards and supporting basic research-activities that are essential in ensuring that legislation, standards, and products are improved continuously.
Although products may be manufactured to National or International Standards, the actual measurements being taken are only as good as the calibration of the instrument used to do the measuring. CoGDEM believes that the correct calibration of products and competent use and maintenance are essential to ensure best monitoring practice.
CoGDEM has written a reference book on all aspects of workplace gas detection including instrument calibration. "The CoGDEM Guide to Gas Detection" should be used in conjunction with specific manufacturer's instructions by trained personnel.
Types of Gasses Monitored by CoGDEM Industrial Sub Group Companies
The CoGDEM Industrial Sub Group members are active in the monitoring of gases and vapours that impact the working and living environment. The common categories of measured gases are described below.
- Flammable gases/vapours
- Toxic gases
- Oxygen and air
- Volatile Organic Compounds (VOCs)
The physical and chemical properties of gases must be understood. When applying gases to check instrument performance it is important to consider the effects of temperature, pressure and humidity, and other factors. For example, heavy hydrocarbon gases respond very slowly and this should be considered particularly when zeroing the instrument after exposure to high gas concentrations. Some gases (such as hydrogen sulphide) may adsorb onto filters or tubing and later desorb back into the sampling system, causing apparent shifts in zero or fault conditions.
Knowing the gas density-is it heavier or lighter than air-helps determine whether the hazard in an enclosed space will be at the top or the bottom of the room. Even in an open, ventilated space it is important to know the density since heavier-than-air gases can remain on the ground or at lower levels. However, density is not the only or sometimes even the major factor that determines gas distribution; for example, escape pressure or air movement due to temperature differences will have an impact on gas distribution when gas escapes.
The chemical activity of different gases varies considerably; for example, methane is not a particularly reactive gas and is difficult to decompose or burn and has a high ignition temperature. Other gases, such as butane, propane, and hydrogen are easily combustible and readily decompose into smaller chemical constituents.
Gases that are less stable (such as chlorine, ozone, nitrogen dioxide, hydrogen sulphide, and sulphur ) will react easily with many common materials. These reactive gases require careful calibration and safety practices. They may react with the materials used in the calibration system-such as tubing, flow meter, etc.-and can be affected by moisture content and other factors in the sampling system. Also, it is important to remember that because their dangerous concentrations are very low, small changes in the sampling system may create large errors in the calibration results.
The flammable limits are of vital importance when measuring gases because they determine the minimum and maximum permissible concentrations of a gas-in-air mixture that will burn under normal conditions of temperature and pressure.
An important feature of a flammable gas, particularly in terms of hazardous area equipment, is its self-ignition temperature. This is the temperature at which the gas-in-air will spontaneously combust with no open ignition source. Hazardous area equipment such as flammable or intrinsically safe gas detectors have a temperature classification, which is the maximum surface temperature that they can attain either under fault or normal operation. It is important that this temperature remains less than the self-ignition temperature of the gas the product will be used in. This topic is discussed fully in a number of publications, particularly in the IEC EN 60079 family of standards.