Gas Selection Guide

Once you've understood a little bit more about the gas you need to detect, visit our homepage to use our product selection tool to find the products that can detect your chosen gas. If your gas is not on our list and you need some help finding a gas detector, please contact our office on 0151 321 0275

Ammonia (NH3) Gas Detection

CAS No.: 7664-41-7

TWA: 25ppm

STEL: 35ppm

Properties: It is a colourless gas with a pungent suffocating odour, which smells like rotten eggs. Ammonia is characterised as a flammable although it is very difficult to ignite. When exposed to heat, an ammonia solution will decompose to form Ammonia gas and oxides of Nitrogen, (NOx).

Dangers: Ammonia will become extremely irritating as concentrations increase. Exposure to high concentrations of ammonia in air causes immediate burning of the nose, throat and respiratory tract, and could cause respiratory distress or failure.

Inhalation of lower concentrations can cause coughing, and nose and throat irritation. Ammonia's odour provides adequate early warning of its presence, but ammonia also causes olfactory fatigue (where the human nose blanks out the smell although the gas remains present), reducing awareness of prolonged exposure at low concentrations.

Where is it found: Ammonia (NH3) naturally exists in humans and in the environment. It is produced naturally from decomposition of organic matter, including plants, animals and animal waste. Ammonia is one of the most commonly produced industrial chemicals. that can be found in a variety of common industrial environments such as fertiliser plants, poultry farms, food processing, refrigeration and chemical plants.


Carbon Dioxide (CO2) Gas Detection

CAS No.: 124-38-9

TWA: 5000ppm

STEL: 15000ppm

Properties: Carbon Dioxide (CO2) is an odourless and colourless gas

Dangers: Despite the fact that we breathe out Carbon Dioxide and that it is present in the atmosphere (about 400 ppm), its maximum safe level is 5000 ppm (0.5% by volume). There is some degree of risk in crowded, badly ventilated places, and an oxygen deficient atmosphere can accompany this problem.

Where is it found: It is a product of combustion and is used to carbonate beer found in brewing and other fermentation processes. CO2 along with Methane are the primary components in landfill and sewage treatment digester gas.

CO2 is heavier than air and collects at low levels. As a guide, Carbon Dioxide gas sensors should be fitted at knee height.


Carbon Monoxide (CO) Gas Detection

CAS No.: 630-08-0

TWA: 30ppm

STEL: 200ppm

Properties: Carbon Monoxide is a colourless gas. To the human senses it is invisible which poses a serious risk. CO is a highly toxic asphyxiant gas.





Dangers: You can't see it, taste it or smell it but CO can kill quickly without warning. Low PPM doses of CO can cause headaches and dizziness. If the victim is removed to fresh air no permanent damages will result. High doses can be fatal.  Levels that do not kill can cause serious harm to health if breathed in over a long period. In extreme cases, paralysis and brain damage can be caused as a result of prolonged exposure to CO. Increasing public understanding of the risks of CO poisoning and taking sensible precautions could dramatically reduce this risk.

Where is it found: Carbon Monoxide is a by-product of combustion and will appear naturally in any situation where burning has taken place. Common applications are steel mills, garages, loading docks, electrical utilities, slaughterhouses, automatic fire suppression systems, food industries, breweries, cellars, laboratories, hospitals, nurseries, climate control and greenhouses.



Chlorine (Cl2) Gas Detection

CAS No. 7782-50-5

STEL: 0.5ppm

Properties: Chlorine (Cl2) is a highly caustic gas with a strong irritating odour

Dangers: Inflammation is caused when Chlorine comes into contact with the skin. When inhaled, Cl2 causes symptoms including coughing, bronchitis and inflammation of nasal mucous membranes.

Where is it found? Chlorine-based solvents such as Chloroethylene or Organochlorine and inorganic Chlorine compounds are widely used as source material in a broad range of products and processes including paper bleach, pulp fibres, medical supplies, pesticides, pigment dye, mineral ore refinement and metal processing. Moreover, urban drinking water which we use every day contains Chlorine as a disinfectant to eliminate bacteria. The work environment at various industrial and public venues where Chlorine is regularly used includes factory emissions measurement and air pollution prevention or at water purification plants, swimming pools.


Chlorine Dioxide (ClO2) Gas Detection

CAS No.10049-04-4

STEL: 0.3ppm

TWA: 0.1ppm

Properties: Chlorine Dioxide is a yellowish-green gas with an acrid odour. One of the most important qualities of chlorine dioxide is its high water solubility, especially in cold water. It remains a dissolved gas in solution.

Dangers:  Chlorine Dioxide is a severe respiratory and eye irritant in humans. Inhalation can produce coughing, wheezing, respiratory distress, and congestion in the lungs.

Where is it found: Over 90% of the ClO2 produced in the world today is made from Sodium Chlorate and is used for pulp bleaching. ClO2 has many applications as an oxidiser or disinfectant such as water treatment and for the disinfection of endoscopes. As a disinfectant it is effective even at low concentrations because of its unique qualities. Sometimes ClO2 is used as a fumigant treatment to sanitise fruit from fungal diseases.


Ethylene Oxide (C2H4O) Gas Detection

CAS No. 75-21-8


TWA: 5ppm

Properties: Ethylene Oxide is a colourless highly water-soluble substance that is in its gaseous state at normal (room) temperature and has an ether-like odour. Its explosive range is very wide with an LEL of 3.0% and a UEL of 100%. With a very low ignition point of -17.8ºC its vapour is volatile enough to explode even in the absence of air / oxygen.

Dangers: Ethylene Oxide is listed as a human carcinogen because it can cause various types of cancer. Exposure to high levels of Ethylene Oxide can cause man problems to human organs. Paralysis and damage the kidneys and liver is common. It can cause emphysema, pneumonia, pulmonary edema, headaches, nausea, vomiting, lack of coordination and memory loss. Ethylene Oxide can severely irritate the eyes, skin, throat, lungs, and respiratory passage. Long-term exposure can cause brain and nervous system problems and cataracts. Exposure to ethylene oxide can cause a pregnant woman to have a miscarriage and may damage the male reproductive glands.

Breathing low levels of ethylene oxide can cause the same health problems but to a lesser degree. Skin contact with ethylene oxide can cause dermatitis, blisters, and burns.

Where is it found? Ethylene oxide is primarily used to make ethylene glycol, which is used to make antifreeze and polyester. Small amounts of ethylene oxide are used in pesticides, insecticides, and fumigants for spices, books, leather, paper, furniture, beekeeping equipment, and transportation vehicles. It is used to sterilize medical equipment and supplies and to purify cocoa, flour, coconut, fruits, dehydrated vegetables, and cosmetics. Ethylene oxide is also an ingredient in textiles, detergents, polyurethane foam, solvents, and adhesives.


Formaldehyde (CH2O) Gas Detection

CAS No. 50-00-0

STEL: 2ppm

TWA: 2ppm

Properties: In chemistry, a 40% formaldehyde solution is called Formalin

Dangers: Recently, it has been found that the fumes given off by phenol resin based adhesives have become a big problem. In a state of solution, it irritates the skin and hardens it until it cracks, and can cause ulcers. In its gaseous state, it irritates the eyes and when inhaled, the mucous membranes, causing coughing fits. Chronic effects include hepatic (liver) and renal (kidney) disorders.

Where is it found? Formalin is used as a raw material for various resin compounds, for sterilisation procedures, as a disinfectant, and antiseptic, and in biochemical laboratories. Besides environmental measurement at various types of manufacturing facilities, measurement inside residential premises is quite common.


Hydrogen Chloride (HCl) Gas Detection

CAS No. 7647-01-0

STEL 5ppm

TWA 1ppm

Properties: Hydrogen Chloride (HCl) is a colourless to slight yellow corrosive gas with a pungent irritating odour.

Dangers: HCl is a strong irritant to the eyes, nose, and upper respiratory tract. Levels of 35 ppm can cause irritation to the throat even after a very short period of time. Contact with eyes or skin causes inflammation. When inhaled, it irritates mucous membranes in throat or nose, and causes coughing. When substantial amounts are inhaled it can cause pulmonary oedema and even death.

Where is it found: In nature Hydrogen Chloride occurs in volcanic gas and in the human body's gastric juices as hydrochloric acid (HCl dissolved in water). It can be produced by the direct reaction of Hydrogen and Chlorine, or in a laboratory by dripping concentrated Hydrochloric acid into a strong Sulphuric acid solution.

Its main uses are in the production of: medical supplies, pigment dye intermediates, inorganic chlorides, chloroethylene (i.e. vinyl chloride), methyl chloride as well as etchants (i.e. etching solutions). Hydrogen Chloride detection is needed in all chemical plants, semiconductor fabrication facilities, oil refineries, where HCl is generated or discharged in the context of chemical reactions or combustion.


Hydrogen Sulphide (H2S) Gas Detection

CAS No. 7783-06-4

STEL: 10ppm

TWA: 5ppm

Properties:  Hydrogen Sulphide is a colourless, toxic, flammable gas that is known by its characteristic rotten egg like odour.

Dangers:  One of the drawbacks to trusting the senses (olfactory) for protection against Hydrogen Sulphide is that prolonged exposure to the gas renders the sense of smell. H2S reacts with the enzymes in the blood stream which inhibit cell respiration. In other words, high concentrations of H2S can shut off the lungs. Low concentration exposure to the gas can burn the respiratory tract and cause swelling around the eyes.

Where is it found:  Hydrogen Sulphide is generated through the hydrolysis of sulphide salts especially where bacteria break down organic matter in the absence of oxygen, e.g. in swamps, sewers, rivers, harbours, etc. It also occurs as a manmade by-product in such industrial facilities as chemical plants, paper mills, oil refineries, etc.


Hydrogen Cyanide (HCN) Detection

CAS No. 74-90-8

STEL: 10ppm

Properties: Hydrogen Cyanide is a colourless to a pale blue liquid or gas. It has a distinct bitter almond-like odour.

Dangers: Hydrogen Cyanide is particularly dangerous because of its toxic/asphyxiating effects on all life requiring oxygen to survive. Hydrogen Cyanide (HCN) is one of the most lethal poisons, being twice as toxic as Potassium Cyanide. It can be fatal not only when swallowed, but, even when it merely comes into contact with the skin. Hydrogen Cyanide poisoning acts quick, it takes between a few seconds and a maximum of 30 minutes for a fatal dose (300ppm or more) to kill an adult. Hence, any emergency first aid measures must be immediately and swiftly initiated.
When the gas is inhaled it may cause headaches, dizziness, ringing in the ears, or vomiting and in severe cases, unconsciousness, or even death.

Where is it found? It is chiefly used as a source material for various organic compounds such as Acrylonitrile, or for Potassium Cyanide as well as in insecticides/pesticides, etc. Primarily at chemical plants where Hydrogen Cyanide is in use or ironworks, metal-plating plants, etc. where Hydrogen Cyanide is generated


Isocyanate Detection

‎CAS Number‎: 584-84-9 (TDI)

CAS Number‎: 26447-40-5 (MDI)

CAS Number‎: 822-06-0 (HDI)

Dangers: While the use of isocyanates is common, worker exposure to isocyanates can be hazardous. Toluene Diisocyanates (TDI) and Methylene Diphenyl Diisocyanate (MDI) detection capabilities should be in place whenever these chemicals are in use. Exposure to isocyanates can cause occupational asthma, irritation of the skin, eyes, nose and throat, and cancer. Deaths have occurred from high dose exposures to isocyanates. Respiratory illnesses also can be caused by isocyanate exposure to the skin.

Where are they found? Isocyanates are widely used in industry. The two most common forms are Toluene Diisocyanates (TDI) and Methylene Diphenyl Diisocyanate (MDI), which are used primarily in polyurethane manufacturing for products such as insulation, mattresses, furniture and car seats. They are also used in spray-on protective coatings, adhesives, paints, and varnishes.


Nitrogen Oxides (NO) Detection

CAS No. 10102-43-9

STEL: 1ppm

TWA: 300ppm

Properties: Nitrogen Oxides (NOx) is a generic term for any of a number of different Oxygen compounds (known as Oxides) of Nitrogen that are given off during combustion, including Nitrogen Monoxide (NO) and Nitrogen Dioxide (NO2).

Dangers: It is extremely rare for Nitrogen Monoxide (NO) or Nitrogen Dioxide (NO2) to be present without the other. Nitrogen Dioxide is toxic and, in high concentrations, strongly irritates eyes, nose, and throat, causing a cough or even pharyngalgia at times, dizziness, headaches, or nausea at times. 

If a large quantity is inhaled, the lips turn blue 5-10 hours later, and cyanosis may occur in addition to pulmonary oedema. Even low concentrations generally becomes a problem and raises chronic bronchitis, gastrointestinal dysfunctions, teeth problems and sleep disturbance as chronic symptoms. In addition, it weakens the body's immune system.

Where is it found? Today, their primary sources include automobile exhaust and factory emissions; although heating and cooking fumes do their part as well. Similar to Sulphur Dioxide, it is primarily measured continuously as part of air pollution and monitoring controls.  Furthermore, it is also frequently measured at the source of industrial emissions or automobile exhaust.


Nitrogen Dioxides (NO2) Detection

CAS No.10102-44-0

STEL: 5ppm

TWA: 3ppm

Properties: Nitrogen Dioxide is a yellowish-brown gas with a characteristic pungent, acrid odour. NO2 is soluble in water at which time it reacts to form nitric acid.

Dangers: NO2 exposure in low doses can cause irritation of the eyes and throat, headache, nausea, and gradual loss of strength. High doses of NO2 can cause pulmonary edema (water in the lungs) and death.

Where is it found? NO2 can be found in industries where the burning of diesel fuel takes place. The most toxic component in diesel emissions is Nitrogen Dioxide.


Oxygen (O2) Detection

CAS No. 7782-44-7

Properties: The oxygen content in air is about 21%, in water 88.8%, and in the human body it is about 65%.

Dangers: Not enough oxygen in the ambient air can be fatal, causing hypoxia (deprivation of an adequate oxygen supply for the body. On the other hand, excessive oxygen in the air poses a fire hazard as it lowers the combustion temperature of flammable materials, and it serves as an accelerant.

Where is it found: Oxygen is the most abundant naturally occurring gas which is discharged into the atmosphere through the process of plant photosynthesis. It is consumed during the respiration process of flora and fauna, photosynthesis in plants, as well as combustion processes. Essentially, oxygen concentrations are measured in working environments to prevent hypoxia incidents; particularly sites where air often stagnates; for instance: manholes, workshop pits, storage tanks, silos, sewer pipes/conduits, warehouses, holds or galleys (on ships), etc. Typically, measurement of oxygen is required to be conducted before the day's work begins and as necessary throughout.


Ozone (O3) Detection

CAS No. 10028-15-6

STEL: 0.2ppm

Properties: Ozone is a non-flammable gas that is typically colourless to blue in colour. It has a very pungent odour.

Dangers: Ozone attacks the eyes and respiratory system and can cause pulmonary oedema. Victims should be removed from the area immediately and given 100% oxygen. When 0.1ppm of ozone is inhaled for two hours, the lung capacity can decrease by 20% or so. Headaches or bronchitis may result when a concentration of 1ppm is inhaled for six hours. 

Where is it found: Ozone is commonly found in wastewater treatment plants, power generation plants and uses include sterilisation, disinfection, bleaching, and as an oxidant and such in organic synthesis. Ozone is typically formed around high-powered electrical equipment where sparking is evident such as welding.  

Interesting Fact: Although the ozone layer in the atmosphere (approximate O3 concentration: 0.005ppm) protects the earth from the sun's ultraviolet light, at ground level in coastal regions (where ultraviolet light is particularly intense) 0.05ppm of ozone can be found.


Phosphine (PH3) Detection

CAS No. 7803-51-2

STEL: 0.2ppm

TWA: 0.1ppm

Properties: Phosphine is a colourless and highly toxic gas with a fishy or garlic-like odour or that of decaying fish. It should also be recognised that phosphine is highly flammable and may spontaneously ignite in air or even explode when mixed with oxygen. Phosphine coming into contact with oxidisers, halogenated hydrocarbons, or even aluminum and copper may cause the same. It is for this reason that extreme care must be adhered to whenever working with or around phosphine.

Dangers: Phosphine acts on the central nervous system and lungs leading to pulmonary oedema. Symptoms like faintness, vomiting, headache, tightness in the chest may appear rapidly after exposure. Even a short exposure to an acute amount of phosphine can lead to chronic neurological problems.

Where is it found? Phosphine is used as an insecticide for the fumigation of grains and animal feed


Sulphur Dioxide (SO2) Detection

CAS No. 7446-09-5

STEL: 5ppm

TWA: 2ppm

Properties: Sulphur Dioxide (SO2) is a colourless gas with a characteristic, irritating, pungent odour.  Sulphur Dioxide gas (sometimes referred to as sulphurous acid gas).

Dangers: Sulphur Dioxide is a highly toxic gas which poisons its victims via inhalation through the lungs. SO2 combines with water to form sulphuric acid. It is for this reason SO2 can burn the respiratory tract upon inhalation. High concentrations cause severe irritation of eyes, nose, and throat. When it dissolves in the water content of the skin, a corrosive acid (sulphurous acid) is formed. Prolonged exposure can cause pulmonary oedema seriously affecting the respiratory process. Death can occur rapidly when exposed to high doses of Sulphur Dioxide.

Where is it found: It is produced industrially when compounds containing sulphur, such as fossil fuels like coal are burned.

Methane Detection

CAS No. 74-82-8

Properties:  Methane, a colourless and odourless gas has long been known as a chief ingredient of swamp gas. It is flammable and when mixed with air can become volatile enough to explode.

Dangers: Methane in itself is harmless, but when its concentration rises, the oxygen concentration falls which can cause hypoxia. It also poses a serious explosion hazard, as it is easily ignitable; (explosive hazard range 5.0-15.0%)

Where is it found? Methane gas is formed as organic matter in the mud of marshes or other wetlands. Methane gas is one of the highest causes of greenhouse gas emissions produced by cattle. Methane often accumulates in underground passageways/conduits (including mine shafts and sewers).


Trichloroethylene Detection

CAS No. 79-01-6

STEL: 150ppm

TWA: 100ppm

Properties:  Trichloroethylene is very volatile and in its liquid state at normal temperatures

Dangers: Trichloroethylene irritates eyes, nose, and throat while repeated skin contact may cause dermatitis. Headache, dizziness, nausea is caused when it absorbs water vapour and it may even cause liver damage. In addition, nausea, diarrhea, hepatic disorders, etc. can occur if trichloroethylene is swallowed.

Where is it found? It is commonly used to degrease metal machine parts and when it seeps underground it sometimes contaminates wells or groundwater which is increasingly becoming a problem in recent years.

How is it detected? Detector tubes are primarily used to measure effluent or groundwater in the context of occupational hygiene management, water contamination/pollution research and prevention, as well as gas emission concentrations.


Arsenic Detection

CAS No. 7440-38-2

Properties:  Arsenic is a fairly common fragile crystalline metalloid ranging in colour from silver-white to black. All compounds containing arsenic are toxic and when they come into contact with acid or acid vapour, a highly toxic gas (arsine) occurs.

Dangers: It frequently affects the function of the digestive organs, causing loss of appetite, convulsions, nausea, constipation or diarrhea, hepatic disorders, and in severe cases, blood may be vomited up or found in feces, leading to a state of collapse or shock, and in extreme cases may be fatal. Moreover, it is considered to have carcinogenic effects on skin, lungs, and liver, too.

Where is it found? Arsenic can be produced industrially through a chemical reaction using carbon to reduce arsenious acid in to its elements. Arsenic is mainly used in insecticides, herbicides, desiccants, and in semiconductor fabrication.


Hydrogen Peroxide Detection

CAS No. 7722-84-1

STEL: 2ppm

TWA: 1ppm

Properties:  Hydrogen Peroxide is a clear, unscented and oily liquid that is water insoluble. It can be extracted with mercury oxide after dissolving α-ethyl anthraquinone in an industrial solvent and oxidising in a (redox reaction). In general, hydrogen peroxide is commercially available as a 30% solution. 
It also interacts as a reducing agent and a powerful oxidiser. When metal catalysts in fine particle form (e.g. copper, silver or platinum) trigger decomposition, high concentrations of oxygen/steam are produced that can combust explosively. 

Dangers: It is highly caustic to skin and mucous membranes, while a 30% solution can cause severe inflammation of eyes and skin upon contact. It is commonly known, that in work environments where Hydrogen Peroxide is in use, exposure to the vapour can have a bleaching effect on hair. If larger quantities are ingested, gastritis and acute toxic effects such as esophagitis, and chronic toxicity symptoms are likely.

Where is it found? Hence, Hydrogen Peroxide is used in 3% solutions not only as a disinfectant, or a bleaching agent for paper, pulp, and natural fibres but, also as an oxidiser, steriliser, reducing agent, and even as liquid rocket fuel.


Styrene Detection

CAS No. 100-42-5

STEL: 250ppm

TWA: 100ppm

Properties:  Styrene, also known as vinyl benzene is a colourless oily liquid that evaporates easily and has a sweet smell. High concentrations have a less pleasant odour. Heavier than air.

Dangers: Styrene is regarded as a hazardous chemical. Short-term exposure to styrene in humans results in mucous membrane and eye irritation, and gastrointestinal effects. Long-term exposure to styrene in humans results in effects on the central nervous system such as headache, fatigue, weakness, and depression, hearing loss, and peripheral neuropathy

Where is it found? Styrene is a flavouring ingredient found in alcoholic beverages. 

Styrene is present in cranberry, currants, grapes, vinegar, parsley, milk and dairy products, whisky, cocoa, coffee, tea, roasted filberts and peanuts. Polymers are used in ion-exchange resins in food processing.

Styrene is primarily used in the production of polystyrene plastics and resins. Styrene is used to make rubbers, polymers and copolymers, and polystyrene plastics.