How and Why Do You Classify a Confined Space?

Here we explain why you may want to classify your entries and discuss two of the most commonly used classification systems in the UK at the moment.

Why do you need to classify ?

In short - you don't need to!

Once you have determined whether your entry is a confined space or not, there is no further legal requirement to classify your space as low, medium, high or 1, 2 , 3 etc.  There is no HSE guidance on classification schemes and despite what some organisations may say, there is no national classification scheme.

However, if done properly, classifying your confined space entry can be useful and can help to:

  • identify equipment requirements,
  • allocate a range of controls
  • specify competency requirements,
  • group hazard types together,
  • benchmark your activities.

If you do decide to classify your entry - make it useful!

What classification systems are there ?

There are numerous classification systems out there.  Some complicated, some simple, some that relate to risk, some that relate to competency.  Whatever system you choose - make it relate to something - make it useful!

If you are starting with a blank canvas I suggest looking at two of the most commonly talked about classification schemes in the UK at the moment, the Water UK NC's and the City and Guilds scheme.  Both of these are summarised below.

Water UK in their Occasional Guidance Note, "The Classification and Management of Confined Space Entries", define confined space entries under 4 categories, NC.1 to NC.4. 


NC.1 - Low risk shallow entry with adequate natural or mechanical ventilation, where access is simple and unobstructed and there is no likely risk of flooding, e.g. meter pits, valve chambers, booster pumping stations, PRV chambers.


NC.2 - Vertical direct unobstructed access with continuous access to a man riding hoist or similar mechanical rescue device.



NC.3 - When it is not possible to have persons attached to a safety line.  Usually it will be a team entry that moves away from the entry point, e.g. man entry sewers, utility subway service tunnels, aqueducts and complex wet wells.  Working without an attached rescue line and away from the point of entry.


NC.4 - Non standard entries involving complex operations which include additional risks and require specific controls and rescue arrangements, e.g. mechanical hazards, physical complexity of system introduced hazards, enhanced specific intrinsic hazards.


The City and Guilds 6150 competency assessment scheme uses a risk based approach.  In summary:

Low Risk entries do not require the use of escape breathing apparatus, either because the risk of a hazardous atmosphere is very low or the time taken to get out of the space would be less than the time taken to don an escape set.

Generally these entries will be made by a single entrant, have simple and unobstructed entry/exit, have adequate natural ventilation, have no likely risk of flooding and may involve lone working.

Medium Risk entries require the use of escape breathing apparatus, either because the risk of a hazardous atmosphere is significant or the time taken to evacuate increases risk to entrants, e.g. distance travelled or where there is more than one entrant. There is a realistic expectation of encountering a specified risk either due to the intrinsic hazards or introduced / task hazards.

There will always be one or more people - positioned outside the confined space - who have designated responsibilities for controlling the entry and dealing with emergencies. 

High Risk entries are generally those where full working breathing apparatus is required, either because there is a known hazardous atmosphere or because the risks of a hazardous atmosphere occurring are significant. This may be due to intrinsic hazards within the space or introduced / task hazards.

Other hazards including, the presence of heat, physical hazards (ie awkward/complex access, size restrictions) or other hazards may necessitate classifying the entry as high risk.

High risk entries require the presence of personnel who have designated responsibilities for dealing with emergencies.

The City and Guilds scheme maps directly across to competency requirements - see our article on City and Guilds accredited training.

What does it mean- classify the entry not the space?

In previous years it was the norm to classify the space or the structure you were entering. Over recent years it has become much more common (and best practice) to classify the 'entry'.

For instance, entry into a benign area to:

  • carry out a visual inspection - may not require the use of any breathing apparatus,
  • break into a pipe which may release a hazardous atmosphere -  may require the use of escape breathing apparatus,
  • investigate the source of a leak or use of chemicals which release vapour - may necessitate the use of full working breathing apparatus.

So with this example you can see that the classification of the space may change depending upon the task that is taking place.

What classification system should you use?

Unless your organisation dictates otherwise, there is no requirement to classify your confined space as low, medium high etc.  There is no national standard and the HSE does not offer any guidance on the matter.  However, as we discussed above, classifying your space can be useful for a number of reasons.

Looking at the two systems explained above - the City and Guilds scheme enables direct mapping to competency requirement and therefore has distinct advantages.  The NC classification scheme incorporates excellent confined space safety principals which again offers advantages.

A good compromise would be to classify your entries as low, medium or high and wherever practicable adopt the principals associated with the NC classification scheme.