Confined spaces can be found in almost any industry and activity, from ship building and repair, to general construction and oil and gas facility commissioning and maintenance. Even a seemingly safe place such as a shipping container could be considered by some health and safety professionals as a confined space, depending upon the scenario at hand.

Due to their nature, and the scenarios we find them in, confined spaces can present many varied hazards. If we do not fully understand how to work within and around these spaces, and counter these threats, workforces can suffer consequences including serious injury and even fatalities. Depending on the nature of the hazard, we could even put entire facilities and businesses at risk. So what is a confined space?

Defining confined spaces

A confined space can sometimes have different definitions. The easiest way to think of it is like this. A confined space is any space or object from which entry and exit is difficult. While work can be performed in a confined space, they are generally not designed for human occupancy. This means that work should only be carried out for as short a time as possible, and persons should only enter the confined space if it is absolutely necessary, in order to carry out and complete the job or task. One typical assumption of a confined space that many people make is that they say the space is small, which is not true. Let’s take an example from the oil and gas industry. There are many facilities and refineries that store various oil and gas products in vast tanks or silos. These vessels can be quite large, sometimes over 60 metres in diameter. We can all agree that this is a considerable size. However, if the tank only had one entry and exit point – let’s say a hatch in the roof – then we would define that tank as a confined space. This is because there is only one point of entry and exit. This would be of particular concern if persons had to evacuate the tank in an emergency situation, or a rescue team were required to extract a casualty from this confined space. So far, while I have mentioned tanks, vessels and silos, other examples of confined spaces could include piping, roof spaces and even excavations. So entry to and exit from a confined space can be difficult, therefore presenting a hazard. What other hazards could we potentially face?

The number and type of hazards to consider is quite varied, but this all depends upon the nature of the confined space, as well as what work is being undertaken. Also, many hazards in a confined space are not visible, or immediately apparent. So let us discuss some of the more common issues we may encounter. First, let us discuss the atmosphere within the space. Depending upon what gasses this contains, it can pose many problems. It could be oxygen enriched or deficient, meaning there is too much or too little oxygen present. Too much oxygen increases the risk of a fire or explosion, too little oxygen means the workforce will suffocate in the space. One example of this would be when purging a vessel or pipe using nitrogen gas. The nitrogen would fill the space, removing the oxygen from it. This presents a problem as nitrogen is an asphyxiant, meaning anyone trying to breath in this atmosphere would suffocate. The atmosphere could also be flammable or toxic. A flammable atmosphere could lead to a fire or explosion if the work being conducted produces sparks or heat (such as welding or grinding). Especially in a tank farm or storage area where many tanks and vessels are present, this presents a huge risk of a potentially devastating chain reaction. This could lead to a horror scenario where one mistake destroys an entire facility and wipes out a workforce, maybe even a community. A toxic atmosphere could have severe health effects or even be fatal to the workers. An example could be the presence of hydrogen sulphide gas, otherwise known as H2S. In a high enough concentration, taking in just one breath of H2S can lead to unconsciousness, followed rapidly by death. Lesser concentrations cause irritation of eyes and skin, and an inability to follow commands. This may not seem too serious, until you cannot find your way out of a confined space because you cannot see, as you are constantly rubbing your eyes and cannot understand a verbal command from a rescuer trying to guide you out of danger.


Another major issue with the atmosphere is something called stratification. All gasses have different densities. Some are heavier than air, and some are lighter. This means different gasses will be found in different parts of a confined space, which presents a problem. Imagine a worker performs a gas test at the top of a tank and the gas test comes up negative for any flammable gasses. The problem here is that H2S, for example, is heavier than air, so will naturally sink to the bottom of the tank. In the right concentration with air, this gas will ignite when in contact with a spark or heat source. A competent gas tester (someone who is knowledgeable, able, trained and experienced) will ensure all levels of a confined space are tested to help ensure the entire atmosphere is checked out and safe to enter.

Another hazard we could face could be the contents within the space. We have already talked about atmosphere referring to gasses that may be present, but these spaces could also have liquid or solid contents. For example, farm workers could be working in a silo containing grain, and engineers from a water company may be faced with sewerage or water in a pipe or tank. In the case of solid contents, a sudden collapse or movement of these contents could bury the workers, trapping, crushing or even suffocating them before help could arrive. Liquid contents could produce hazardous vapours, and there is the risk of drowning should a worker fall into the liquid present.

Height is also a potential issue. It may be that the worker is entering a large oil silo through a hatch in the roof; or a worker could be conducting work on the inside of a vertical pipe; it could even be a worker at ground level visually inspecting an underground vessel from street level. One slip or miscalculation, and the worker falls. The height of the fall would partly determine the severity of the consequence, as there may be contents in the tank that exasperate the situation, as mentioned in the previous paragraph. Even if they survived the initial fall, we then face the prospect of putting more personnel at risk to rescue the injured party, potentially increasing the number of victims from the incident.

Size and shape are also parameters that need to be considered. For example, it is very easy to move around the smooth, flat floor, of the inside of a 60 metre wide, 20 metre tall tank. Now consider the difficulty of wriggling round a 90 degree bend in a 1 metre wide pipe wearing SCBA (Self-Contained Breathing Apparatus) Equipment. Even a seemingly simple problem, like someone getting stuck in a hatchway, can cause all kinds of issues. So how can we reduce these risks to as low as reasonably practicable (ALARP) for the workforce?

Hierarchy of controls

Control measures would again depend upon the nature of the space, and the work to be undertaken. You should always follow the hierarchy of controls – eliminate, substitute, isolate, engineer, administrate and PPE – wherever possible, but here are some things to consider. First, is it absolutely necessary for the workforce to go into the space? Using certain equipment or best practice methods may mean the work can be completed from outside the confined space, eliminating the risk to workers. For example, workers could test the atmosphere of a space using probes, or by lowering the testing equipment into a space using rope.

Removing the contents from the space would help eliminate any hazards posed by those contents, but do not be complacent. For example, you may have removed all of the liquid hydrocarbons present in a tank, but there may still be flammable or toxic vapours or residue remaining inside.

As mentioned earlier, gas testing is something we can do in terms of identifying atmospheric hazards. Conducted properly, this will allow us to identify what gasses are present, and what their concentrations are. From there we can plan appropriate actions such as purging the space, replacing the gasses with something less harmful, or removing them altogether. Ensuring proper ventilation could also help to prevent the atmosphere from returning to its previous dangerous condition.

Engineering measures such as isolation flanges, valves and seals could be considered, placing a barrier between hazardous substances and the workforce in the space. An example would be closing valves in piping that lead to a tank or silo, or shoring the sides of excavations, preventing collapse of materials onto workers. Correct equipment for the task at hand is also an important consideration. Do the workers require specific respiratory protective equipment (RPE) to be able to survive in a hazardous atmosphere? Is ventilation equipment powerful enough to move air through the entire space being worked in? Are gas monitors, lights, radios and other equipment non-spark producing or explosion proof? Are workers using personal fall arrest systems (PFAS) or scaffolding to work in high areas?

Administrative safety

Legislation, training and other administrative points would need to be addressed. Legislation, standards and work practices may vary between companies, countries and regions. For example, working to Occupation Safety and Health Administration of America (OSHA) standards may not be acceptable in a company where the policy is to work to the UK’s Health and Safety Executive (HSE) standards. While workers may be familiar with the task to be accomplished, they may not be aware of all the dangers of the confined space they are going to work in. Training, therefore, is an important consideration. Another administrative tool, used especially in oil and gas, is to adopt a buddy system. This ensures that nobody works in and around confined spaces on their own.

Buddy systems

The buddy would be part of a team of two or more workers, and is generally stationed at the entry/exit point of the confined space. This is so that, in some cases, they can observe the workers in the space. More importantly, however, in all cases this means that if something goes wrong, the buddy is in a safe place in order to be able to summon help in an emergency situation. Many major companies have sets of life saving rules, and in some cases, the rules are specific to confined spaces. These could include ensuring gas testing is conducted prior to entry of a confined space, or ensuring a permit-to-work is obtained and authorised before working in a confined space. These rules are as they state, life saving. They are enforced strictly, and any breach of these rules generally leads to a harsh punishment, including termination of employment in some cases. As always thorough risk assessment, and use of tools such as JHAs (Job Hazard Analysis), will help to identify the specific hazards for the specific scenario at hand. So just like any job or task, it is important we reduce the risks to our workforce to be as low as reasonably practicable. But what if it all goes wrong, or something unforeseeable happens?

When the worst happens

A worker is overcome by fumes and falls through a hatch into a tank. A sudden rainstorm flashes through a construction site, weakening the walls of an excavation, causing it to collapse. A worker becomes stuck inside a pipe and is unable to free himself. All nightmare scenarios certainly, and situations where a rescue is required. Performing a rescue in any emergency situation is extremely hazardous, and even if the victim survives the initial incident, it can quickly escalate. Being trapped in a confined space can lead workers to suffer from the effects of claustrophobia, shock, or suffer secondary effects from the hazards of the incident. For example, the worker in the excavation could survive initially being buried under the material, but may suffocate due to lack of oxygen, or perish as a result of crush injuries. Every rescue scenario will therefore be specific to the nature of the work being undertaken and the incidents that are likely to occur.

While we cannot plan for every scenario, it’s a good idea to think of and plan for the worst thing that could possibly happen, and ensure everyone knows the details. While it is difficult to recreate accident and incident scenarios, practicing rescues whenever possible will help ensure personnel, equipment and plans work as expected. Especially working in remote locations, specialist help you may need will not be close by. So it is important to have all the necessary equipment and personnel available, should disaster strike. Anyone who is nominated to be part of the rescue team, should be competent to perform rescues. They should have all the required equipment, including specialist gear such as SCBA, and they must know all the proper procedures. This will ensure that the risk to the rescue team is minimised, as all rescue personnel know who is responsible to do what, when and how. The focus can then be on helping the victims of the incident. Remember, a confined space rescue is a hazardous and complex operation. A competent person must have the correct experience and judgement to decide whether a rescue can, and more importantly, should be performed. It might be that the situation is simply too dangerous to risk the rescue personnel, or the victim of the incident may already be deceased. While this seems a cruel thing to think, we must ensure that we do not unnecessarily add to the list of victims of the incident. Even a body retrieval exercise can be a hazardous operation, and should be planned and performed with extreme care.


So there is a lot more to confined spaces than meets the eye. Remember, there is not a “one-solution-fits-all” fix for confined space hazards. Examine in detail the specifics of the job being performed, and the environment it is to be done in. If needed, seek the advice of consultants, engineers and other specialists. Open your mind to confined space safety, and you will help to maintain a happy, competent, profitable, and most importantly, safe, workplace and workforce.