Oxygen
Properties:
Odourless, colourless and tasteless gas. Can be displaced or diluted by other gases including carbon dioxide and nitrogen as well as other inserting or toxic gases.
Description:
Oxygen content in normal atmosphere is approx 20.9% by volume, the balance is primarily nitrogen.
Health Hazards:
At 15 -19% oxygen impaired coordination and a decreased ability to work strenuously. At 10 -14% respiratory problems. Few recover after more than 5 mins in less then 8% oxygen
Exposure Limits:
Deficiency: 18%
Enrichment: 23%
Typical Applications:
Deficiency: areas subject to oxidation combustion, bacterial growth, oxygen displacement by other gas or purge gases.
Carbon Monoxide
Properties:
Odourless, colourless, chemical asphyxiant with toxic and flammable properties. Flammable above 12.5% by volume.
Description:
Similar density to air, disperses evenly throughout confined spaces. Once CO enters the lungs it disperses instantly into the bloodstream.
Health Hazards:
Acts toxically by preventing the haemoglobin of the red blood cells from carrying the required oxygen to the brain. Above 300ppm produces headaches, fatigue and discomfort.
Exposure Limits:
STEL: 300ppm
TWA: 50ppm
Typical Applications:
Enclosed car parks; coke ovens blast furnaces, fossil fuelled power and heat generators.
Hydrogen Sulphide
Properties:
Colourless gas known for its rotten egg smell. Flammable above 4.3% by volume. The density of hydrogen sulphide is 1.19 relative to air (1.0) and although heavier than air, factors such as air movement, presence of other gases and potential release sources are factors to be considered when determining sensor location.
Description:
By-product of sulphur based processes and decomposition of organic matter, the most commonly encountered toxic gas.
Health Hazards:
At low ppm concentration desensitises the olfactory system in 2-5 mins through sodium sulphide formation. Smell appears to go away even in increasing concentrations. Irritates the eyes and upper respiratory tract at 20-50ppm. Attacks the nervous system at intermediate concentrations. Often fatal respiratory paralysis at concentrations over 1000ppm.
Exposure Limits:
STEL: 15ppm
TWA: 10ppm
Typical Applications:
Mines, spring water, petrol processing and refining, tunneling, sewers, shipping, wood pulp manufacture, vulcanization of rubber.
Nitrogen Dioxide
Properties:
odourless reddish brown gas 1.5 times heavier then air.
Description:
Component of Nox nitrous fumes, a by product of the manufacture of nitric and sulphuric acid.
Health Hazards:
Causes coughing, throat irritation, shortness of breath and more severe respiratory symptoms.
Exposure Limits:
STEL: 5ppm
TWA: 3ppm
Typical Applications:
Diesel generators,waste incinerators chemical processing.
Carbon Dioxide
Properties:
Generally colourless and odourless but may have a slight pungent odour and biting taste.
Description:
Air contains 0.0033% of CO2. A normal by-product of human and animal metabolism, relatively non reactive and non toxic. 1.5 times heavier than air so settles at bottom of confined spaces.
Health Hazards:
Causes headaches, dizziness, increases the heart rate and blood pressure and induces coma.
Exposure Limits:
STEL: 15000ppm
TWA: 5000ppm
Typical Applications:
Chemical industry, textile processing waste water treatment, fermentation processes.
Chlorine
Properties:
Toxic in gas phase,exhibiting a yellow green colour and pungent odour. Liquid chlorine has a transparent amber colour.
Description:
2.5 times heavier than air, remains close to the ground on release. Most produced or manufactured toxic gas existing today.
Health Hazards:
Severe lung and skin irritant. Small concentrations cause burning eyes, coughing, flushed skin, sneezing and hoarseness. Inhalation of higher concentration affects upper and lower respiratory tract and can produce pulmonary Oedema.
Exposure Limits:
STEL: 1ppm
TWA: 0.5ppm
Typical Applications:
Water treatment, swimming pools, chlorine storage areas, paper industry.
Hydrocarbons
Properties:
Wide range of explosive gases, most being heavier than air. Propane is heavier, methane is lighter than air
Description:
Range from simple gases such as methane(CH4)and propane(C3H8) to complex petroleum and
alcohol vapours.
Health Hazards:
Concentrations above LEL present explosion and fire risk.
Exposure Limits:
Depends on Gas
Typical Applications:
Sewage treatment, gas supply utillities, chemical and petrochemical industries land fill sites.