Gas cylinders

The greatest danger presented by bottled gases, which may become exposed to fire or be subjected to radiated heat, is that of explosion and possible fragmentation.

Cylinders can rupture as a result of increased internal pressure and/or the loss of tensile strength of the cylinder metal whether the contents are flammable or not.

Impact may result in rupture or may trigger progressive decomposition, which may ultimately cause the cylinder to explode, e.g. acetylene.

Gases are commonly stored in cylinders in two forms:

1. Compressed gases: These are stored in a gaseous form at high pressures of up to 20 400 kPa in strong cylinders that contain no liquid phase.
2. Liquefied gases: These have properties enabling them to be relatively easily liquefied and stored under not excessively high pressures at ambient temperatures in cylinders containing both liquid and gas in equilibrium.

Bursting temperatures

When cylinders are exposed to fire conditions, temperatures at which they would be in danger of bursting will rapidly be reached.

The following table is an extract from an article The Behaviour of Gas Cylinders in Fires by E G Butcher and C Cilsby, which appeared in the UK publication Fire, in May 1965.

Should a cylinder containing a gas begin to leak, an obvious hazard is introduced and it is important to know the hazardous properties of all gases stored on the premises, to enable proper precautions or remedial action to be taken. This applies particularly to toxic, oxidising or flammable gases.

The following physical characteristics will affect the fire and explosion hazard of flammable gases.

Explosive limits

Gases will burn or explode only when their percentage concentration in the air is within their upper or lower explosive limits e.g. acetylene 2,5% to 82% and butane, 1,9% to 8,5%.  The lower explosive limit is most significant in the case of leakage.

Ignition temperatures

Gases having ignition temperatures below 700ºC can be ignited by open flames or by sparks glowing at temperatures above dull red heat (± 700ºC) while those with ignition temperatures below 500ºC can be ignited by surfaces at black heat (± 300ºC).

Vapour density

Gases lighter than air will rise and disperse easily if not confined, whereas those which are denser than air, disperse less readily, flow along the ground and into drains and low-lying areas. If air is taken as 1 then hydrogen would have a density of 0,07 and butane 2,01.

Storage of cylinders

• Storage areas should be well clear of buildings wherever possible.
• A protective covering should be provided.
• Adequate ventilation should be provided.
• Storage areas should be kept free from all combustible materials. No other materials should be stored in cylinder enclosures.
• Full cylinders should be kept apart from empty cylinders so that it will not be necessary to open valves to check whether cylinders are empty or full. Mark empty cylinders with the letters “MT” to avoid confusion.
• Cylinders should always stand upright. Special stands should be used or cylinders should be chained in the upright position. This will prevent them falling over causing damage to valve assemblies.
• Cylinders should be stored in rows with aisles in between for easy removal in the event of fire.
• For security and ventilation purposes, a wire mesh fence should surround the storage area. Keep the enclosure locked and appoint a responsible person in charge of keys to control the issuing of cylinders.
• Empty cylinders should be immediately returned to the empties store. Before being locked away, a check should be made that valves have been tightly closed.
• Notices prohibiting smoking and naked lights, as well as notices describing the colour code for cylinder contents, should be prominently displayed.
• Where provision exists, fit protective caps over valves when cylinders are not in use.
• Flammable and oxidising gases should not be stored together. Greases and oils must never be allowed to come into contact with oxygen as this could result in spontaneous combustion.
• Inspect all cylinders entering your premises before accepting them to ensure that they are not leaking. Brushing of valve assemblies with a soap solution is recommended for this operation. If a cylinder in the storage area is found to be leaking, move it a safe area and inform the suppliers.
• If a detached storage area is not available and the storage area forms part of a building used for another purpose, the following should apply:
  • Position the store against an outside wall.
  • Segregate the store from the rest of the building by walls having a fire resistance of at least two hours.
  • The external wall should preferably be of light construction to vent an explosion outwards, the proviso being that such venting does not present a hazard to people or property.
  • Doors must only be provided in external walls and should not permit communication with the rest of the building.
  • Ventilate the area at both high and low levels, but if satisfactory natural ventilation cannot be provided, then mechanical ventilation should be installed.
  • If electric lighting is required in the storage area, it should be of an approved type and comply with the SABS Code 0108/1995 – “The classification of hazardous locations and the selection of electrical apparatus for use in such locations”.

Published by
Fire Protection Association of Southern Africa
(Incorporated Association not for Gain)
(Reg.No. 73/00022/08)
P O Box 15467
Impala Park
1472

Gas cylinders.pdf

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Marcel Wood

Marcel Wood heads Etana’s risk management division. Before starting in insurance he worked for the fire department, rescuing people and (literally) putting out fires. He’s passed through Munich Re and Santam, and has designed the only risk management tool aimed specifically at the insurance industry – ARQ. Marcel is a mean guitarist, a brilliant vocalist and an accomplished soccer player with the personal motto: “Do your best all the time”.