A gas detector is a device which detects the presence of various gases within an area, usually as part of a system to warn about gases which might be harmful to humans or animals.
Gas detection falls into two main categories, Safety and Combustion Analysis.
Safety Analysis
Safety applications require the detection of flammable gases, toxic gases and oxygen levels. Many of these gases are both colourless and odourless, hence the need for a gas monitor.
The purpose of a personal gas monitor is to alert the user to potential hazards well before he or she is exposed to gas levels hazardous to health. These levels are set out in the EH40 document covering Occupational Exposure Limits as issued by the Health and Safety Executive.
The commonly monitored gases are Flammables, Carbon Monoxide, Hydrogen Sulphide and Oxygen, although sensors are available for a wide range of other gases.
Combustion Analysis
Combustion Analysis is generally used as a means of determining the efficiency of a fuel burning application, such as a boiler. Levels of unburned fuel, oxygen, carbon monoxide and carbon dioxide, as well as temperature and pressure can be monitored to calculate the efficiency of the combustion.
Definition of Gas Detection TermsFlammable Gases
The Lower Explosive Limit (LEL) of a flammable gas is the lowest concentration of ‘fuel’ in air that will burn. Modern
flammable gas monitors are designed to go into an alarm state at a much lower level, typically 20% LEL, providing the user with adequate warning to shut down plant or evacuate the area.
Toxic Gas Dectection
The Toxic gases most commonly encountered are Carbon Monoxide (CO) and Hydrogen Sulphide (H2S) .
Carbon Monoxide is the most abundant toxic gas and is both colourless and odourless. Maximum safe exposure limits are between 30 to 50 parts per million(ppm), but lower levels have the effect of causing drowsiness. Any process where there is combustion of fuel can lead to the production of
Carbon Monoxide (
CO) /
Hydrogen Sulphide (
H2S) is well known due to its bad egg odour. This can be smelt at levels as low as 0.1ppm. The maximum safe exposure limit is 10ppm, however, higher concentrations of
Hydrogen Sulphide cannot be smelt and can lead to instant paralysis.
Oxygen Levels
The usual concentration of oxygen is 20.9%. Unless there is adequate ventilation, the level is reduced surprisingly quickly by breathing, combustion or dilution by other gases. Most gas detectors provide a low alarm at 18% or 19%. People behave abnormally when levels reach 17%, with death coming quickly if the level drops only 2 or 3% more. Exposure to oxygen levels between 10% and 13% can bring about unconsciousness so quickly that the individual cannot help or protect him/herself.
Oxygen enrichment dramatically increases the flammability of anything, which will burn. If levels exceed 24%, then materials such as clothing, which might normally smoulder, will burst into flame. The Tragic Deaths of the
Apollo 1 Crew is an example of the safety problems caused by a high oxygen environment - Albeit in a pure Oxygen environment.
Typical Gas Detection Applications· Oil Rigs and Platforms, Refineries and Petrochemical Plant
· Confined Spaces
· Risks in Tanks, Sewers, Containers and Holds
· Steel Industry
· Fire Brigades
· Storage Areas
· Marine and Vehicles
· Power Generation
· Boiler Monitoring
· Fire and Gas Detection for Turbines
· Fire detection in Coal Silos, Feeders, Mills and Classifiers
· Protection of Personnel
· Waste Disposal and Landfill Sites
· Emission Monitoring
· Digester Gas Monitoring
· Everyday Places – e.g. Boilers in hospitals, hotels, schools etc.
