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A Guide to Confined Space Hazards

2nd September 2019
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Confined spaces have the potential to become dangerous places to work in, and it is important that anyone working in a confined space understands possible hazards that could arise.

A confined space is defined as:

“Any place, including any chamber, tank, vat, silo, pit, trench, pipe, sewer, flue, well or other similar space in which, by virtue of its enclosed nature, there arises a reasonably foreseeable specified risk”

Confined spaces have two defining features:

  1. They are places which are substantially (though not always entirely) enclosed
  2. There is a reasonably foreseeable risk of serious personal injury from hazardous substances or conditions within the space or nearby

Confined space regulations provide a hierarchy of preventing injuries due to hazards:

Common Hazards in Confined Spaces  

There are many potential hazards and risks associated with working in a confined space.

A hazard is anything that has the potential to cause harm. When taken in isolation, a hazard is not harmful, it is the interaction with something else (e.g. a person) that raises the potential.

There are a number of specified risks associated with confined spaces as shown below:

Specified Risk

Example of hazardous situations

Asphyxiation from free-flowing solids

  • Working in a silo on a farm that contains grain – you can be completely submerged by grain in seconds

Fire or explosion

  • Performing repairs and maintenance work in a boiler or tank that involves flame cutting or welding operations
  • Flour mills – flour is very flammable when it is airborne, so controls need to be in place to stop any igniting material coming into contact with flour or dust

Loss of consciousness or asphyxiation from gas, fume, vapour or lack of oxygen


  • Waste recycling plants that burn household waste to generate electricity can produce methane, hydrogen sulphide, ammonia and carbon dioxide gas
  • Workers that are in an environment where rust is present, such as tanks, where there is little air movement that can then lead to lack of oxygen

Potential for drowning due to increase in liquid

  • Any manufacturing process that uses tanks of water, could see rising water levels due to poor isolation. If people work in a tank that is usually filled with water, the water needs to be isolated before work begins, but if it isn’t done correctly the water could enter whilst they are working inside
  • If there is heavy rainfall and/or leaking pipework, there could be rising water levels in sumps

Loss of consciousness due to increase in body temperatures

  • Working in metal tanks, boilers or pipes that naturally get hot if the outside temperate is hot – it can bake the pipes which workers have to enter. If the area is not cooled down enough to work in, your internal body temperate will increase quite quickly. This was the case at a bakery company when workers entered a large oven before it had been properly cooled. They died of heat exposure


There are other hazards that can be encountered when working on site – they are not specific to confined space work although can occur – please note this is not an exhaustive list

  • Electric shock
  • Contact with contaminated soil
  • Falls from height
  • Slips & trips
  • Manual handling
  • Poor communications
  • Poor lighting
  • Lack of supervision
  • Contact with moving vehicles / machinery
  • Falls of ground, roof, sides and open face of any excavation
  • Rat poison from rodent control can cause ill effects – can affect body’s ability to clot blood
  • Leptospirosis (Weil’s disease) caused by contact with infected animal urine (e.g. rats) can cause a variety of symptoms and in extreme cases, can prove fatal.

How to Minimise the Risk of Hazards and Injuries

If persons need to enter and work in a confined space, then it is a requirement that hazards are identified and control measures put in place to control each hazard.

A risk assessment is a procedure carried out prior to the commencement of work. It looks at hazards (anything that may cause harm) and the risks (chances that someone could be harmed by the hazard). Its purpose is to identify potential hazards to persons whilst carrying out a task from which it is possible to take precautions to control these hazards.

The hazards and precautions identified are in most cases required to be recorded by law, specifically required under a wide range of legislation including: -

  • The Control of Noise at Work Regulations 2005
  • The Control of Substances Hazardous to Health Regulations 2002
  • The Personal Protective Equipment at Work Regulations 1992
  • The Manual Handling Operations Regulations 1992
  • The Control of Vibration at Work Regulations 2005
  • The Work at Height Regulations 2005
  • The Lifting Operations and Lifting Equipment Regulations 1998
  • The Dangerous Substances and Explosive Atmospheres Regulations 2002

There are 5 steps to risk assessments:

1. Identify the hazards

2. Decide who might be harmed and how

3. Evaluate the risks and decide on precautions

4. Record your findings and implement them

5. Review your risk assessment and update if necessary

If you would like to learn more about confined space risk assessments, take a look at our ‘What is a Confined Space Risk Assessment’ guide. By identifying hazards, controls and problems that may need to be remedied before work commences – it should be possible to minimise the risks of hazards harming people.

Our specialist teams provide risk assessments and consultancy – to help businesses identify hazards and keep their employees safe. As confined space experts, with over 100 years of experience in mines rescue – we know how important it is to make sure any person working in a hazardous environment has the right training and is aware of potential risks.

Contact us if you would like to discuss how we can help your business mitigate hazards, risks and improve workplace safety.

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