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Safety information

All gases will diffuse in air. Gases that are lighter than air, such as natural gas rise, mix with air and dissipate quite quickly. Gases that are heavier than air, such as LP Gas tend to collect at the lowest point. If LP Gas builds up on the ground or in a confined space, dissipation will be slower as air may be in contact only with the surface of the gas.

For escaping gas to be a fire or explosion hazard, there must be gas (fuel) and air (oxygen) in the correct proportions and an ignition source.

Image showing components of an explosion as fuel, oxygen and ignition

Reactions

For normal methane or propane combustion the reactions can be shown as:

Image showing the text of a formula

and

Image showing the text of a formula

But where there is insufficient oxygen (air) the reaction for methane will also include:

Image showing the text of a formula

Flammability limits

Not all air-gas mixtures are combustible. Air-gas mixtures will only burn or explode within certain limits, known as the flammable (explosive) limits.

The lower explosive limit (LEL) is the minimum percentage of gas mixed with air that will burn or explode. The LEL for natural gas is 5% gas to 95% air. The LEL for LPG is 2.5% gas to 97.5% air.

The upper explosive limit (UEL) is the maximum percentage of gas mixed with air that will burn or explode. The UEL of natural gas is 14% gas to 86% air. The UEL for LPG is 9.5% gas to 90.5% air.

Odorant

All hydrocarbon gases have odour added before distribution to the customer. The amount of odorant is specified in the Gas Standards (Gas Supply and System Safety) Regulations 2000. Some of the compounds used to odorise gas are different but their smell is similar. A common constituent of odorants is Ethyl Mercaptan and it is very smelly. The amount of odorant that is added to the gas must be sufficient to make a mixture of one-fifth of the LEL detectable by smell.

Nature of hazard

Gas is a safe and efficient source of energy when used properly. Gas appliances and installations incorporate in their designs safety features to protect people and property from malfunctions (usually with appliances). However, without proper installation and use, the potential exists for the appliance not to function correctly.

The hazards of escaping unburnt gas are:

  1. Fire
  2. Explosion
  3. Asphyxiation

The hazards of partially burnt gas are:

  1. Asphyxiation
  2. Carbon Monoxide Poisoning

What to do if you can smell gas in a building

Smells of gas in a building are not normal and steps must be taken to eliminate a hazard or potential hazard that could arise from leaking gas. The points below offer general information on making the situation safe. However, gas suppliers' instructions should always be followed.

  1. Turn off the supply of gas to the building at the meter or cylinder. Don't assume that turning off at the meter will stop the leak, as it may be coming from a nearby main or service.
  2. If you consider it necessary, evacuate the building.
  3. Eliminate ignition sources by extinguishing any naked flames, preventing smoking, preventing striking of matches and lighters and by not touching any electrical switches.
  4. If lights are on, leave them on.
  5. Ventilate the building by opening all the doors and windows.
  6. Notify the gas supplier. If some of the other factors are more urgent, ask someone else to make the call to the gas supplier.
  7. Do not enter the gas-affected area.

Safe use of liquefied petroleum gas

Refer to EnergySafety publications.

Effects of carbon monoxide poisoning and asphyxiation on the body

Carbon monoxide combines with haemoglobin in blood and is pumped around the body. This prevents the blood from carrying oxygen and starves the body tissues. Even small concentrations of carbon monoxide can be lethal. One part carbon monoxide in one thousand can kill. Incomplete combustion with any gas-burning appliance may produce carbon monoxide, hence the importance of locating, installing commissioning and operating appliances correctly.

Some of the symptoms that may be present in a person suffering from the effects of inhaling carbon monoxide include:

  1. Giddiness
  2. Lack of control of the muscles
  3. Shortness of breath
  4. Semi consciousness
  5. Lips, nose, ears and cheeks becoming a bright cherry red colour.

People suffering carbon monoxide poisoning may have a sense of well being and insist that they are all right even though the above symptoms are evident. This is because their system "feels" well oxygenated.

If Natural Gas or LP Gas escape and builds up in an open area, gas may build up at the expense of air. The exclusion of oxygen in an area can have a very quick effect on a person in that area. Asphyxiation is a lack of oxygen in the blood.

Some of the symptoms of asphyxiation include:

  1. Faintness
  2. Weakness
  3. Partial or complete lack of consciousness
  4. A sense of well being and may react aggressively if asked if feeling alright.
  5. Lips and cheeks becoming a blue colour.
  6. All facial features will become blue in colour but the person may be unconscious at this stage.

Resuscitation

To treat a person who is affected by carbon monoxide or asphyxiation, first move them to a gas free area. Then begin to resuscitate being careful not to inhale exhausted air from the patient. Call an ambulance.