CS : Confined Space : Hazards & Controls

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Chapter : Confined Space 

Confined Space : Hazards & Controls 

Confined Space refers to any place, including any vessel, tank, container, pit, bund, chamber, cellar or any other similar space which, by virtue of its enclosed nature, creates conditions that give rise to a likelihood of an accident, harm or injury of such a nature as to require emergency action due to the presence or reasonable foreseeable presence of:

• Flammable or explosive atmospheres
• Harmful gas, fume or vapour
• Free flowing solid or an increasing level of liquid
• Excess of oxygen
• Excessively high temperature
• Lack or reasonably foreseeable lack of oxygen.

Hazards associated with confined spacesinclude:

Toxic Atmosphere

A toxic atmosphere may cause various acute effects, including impairment of judgement, unconsciousness and death. A toxic atmosphere may occur due to the presence or ingress of hazardous substances. These substances may be present in the Confined Space for various reasons such as:

• Remaining from previous processing or storage
• Arising from the disturbance of sludge and other deposits
• The presence of a fire or flames within the space
• Seepage from improperly isolated adjoining plant
• Formation during the work processes carried out in the space
• Being released from under scale and in brickwork as a result of the work process

Oxygen Deficiency

Oxygen can be lacking a confined space for the following reasons:

• Displacement of air by another gas
• Various biological processes or chemical reactions (such as rotting of organic matter, rusting of metals, burning, etc)
• Absorption of air onto steel surfaces, especially where these are damp

Oxygen Enrichment

An excess of oxygen, in the presence of combustible materials, results in an increased risk of fire and explosion. Some materials, which do not burn in air, may burn vigorously or even spontaneously in an enriched oxygen atmosphere.

Flammable or Explosive Atmospheres

A flammable atmosphere presents a risk of fire or explosion. Such an atmosphere can arise from the presence in the confined space of flammable liquids or gases or of a suspension of combustible dust in air. If a flammable atmosphere inside a confined space ignites, an explosion may occur, resulting in the expulsion of hot gases and the disintegration of the structure.

Flowing Liquid or Free Flowing Solids

Liquids or solids can flow into the confined space causing drowning, suffocation, burns and other injuries.  Solids in powder form may also be disturbed in a confined space resulting in an asphyxiating atmosphere.

Excessive Heat

The enclosed nature of a confined space can increase the risk of heat stroke or collapse from heat stress, if conditions are excessively hot. The risk may be exacerbated by the wearing of personal protective equipment or by lack of ventilation.

Key elements of a safe system of work for a confined space

The key elements to be considered when drawing up a safe system of work are:

• Competence, training, supervision and suitability
• Permit-to-work procedure
• Gas purging and ventilation
• Dangerous residues
• Testing and monitoring of the atmosphere
• Mechanical, electrical and process isolation
• Respiratory protective equipment
• Other personal protective equipment
• Safe use of work equipment
• Communications
• Access and egress
• Flammable or explosive atmospheres
• Combustible materials.