A space is confined because of the RISK in it, not because it is small. The regulations define it as any place which, by virtue of its enclosed nature, creates a reasonably foreseeable specified risk, and then set an order that is stricter than almost anything else in health and safety: do not enter if the work can be done from outside, and if entry is unavoidable, have both a safe system of work and the emergency arrangements ready before anybody goes in.
Confined space risks, the five specified ones and the sixth
The regulations list five specified risks and a space is confined only if one of them is reasonably foreseeable. Serious injury from fire or explosion. Loss of consciousness from an increase in body temperature. Loss of consciousness or asphyxiation from gas, fume, vapour or a lack of oxygen. Drowning from a rising level of liquid. And asphyxiation from a free flowing solid, or being unable to reach a breathable environment because a free flowing solid has trapped you. The sixth risk is not in the regulations and kills more people than several of the others: the rescuer. A large share of confined space fatalities are colleagues who went in after the first casualty without equipment, which is precisely why the emergency arrangements have to exist before entry rather than being improvised at the moment somebody collapses.
What confined space work means, and what is not one
The examples in the regulations are a chamber, tank, vat, silo, pit, trench, pipe, sewer, flue or well, and similar spaces. Size and access are not the test: a large room with a nitrogen leak can be a confined space and a small cupboard with an open door is not. Two consequences catch people out. A space can be confined ONLY SOMETIMES, for instance a pit that is safe until somebody starts welding in it or a cellar that is safe until a carbon dioxide cylinder is changed, so the assessment is about the work as well as the place. And some obvious looking spaces are not confined spaces at all once the specified risks are honestly considered, which matters because treating everything as a confined space devalues the controls that the real ones need.
Confined space medium risk, and why the classification matters
Low, medium and high risk are not legal categories: they come from the training and competence schemes the industry uses, and they map to the equipment and the rescue provision rather than to a legal duty. Broadly, low risk covers a space with adequate natural ventilation, a large opening and no foreseeable atmosphere problem, where escape is straightforward. Medium risk introduces restricted access or a foreseeable atmospheric risk, so escape breathing apparatus, gas monitoring, a top man and a means of extraction from the space become the norm. High risk means access so restricted, or an atmosphere so hazardous, that entry needs full breathing apparatus and a dedicated rescue team on site. The classification matters because it is what a client's permit and an operative's certificate are written against, and because a team trained and equipped for medium risk cannot lawfully be sent into a high risk entry.
Working in a confined space, and the safe system it takes
The safe system is a list and every item earns its place. A specific assessment of THIS entry, not a generic one. A permit to work naming the space, the task, the duration and the people. Isolation and lock off of anything that could fill, start, heat or electrify the space, proved rather than assumed. Atmosphere testing before entry and continuous monitoring during it, for oxygen, flammable gas and the specific contaminants expected. Ventilation. Access and egress arrangements including a retrieval line and body attachment where recovery from outside is possible. Communication that works from inside. A top man who does not enter. A rescue plan with the equipment present and people trained to use it. And no lone entry. Where any one of those cannot be provided, the honest answer is that the entry does not happen that day, which is also the cheapest answer available.
Confined space working, and the permit that controls it
A permit is how the safe system stops being a document and starts being a control. It names the space, the task, the people and the duration, and it is issued by somebody authorised who has confirmed each precondition rather than assumed it: isolations in place and proved, atmosphere tested with the readings written on the permit, ventilation running, communications tested, the retrieval arrangements in place, the rescue team or equipment present, and everybody briefed. It has a time limit, and it is handed back and closed, which is the step that accounts for the people, because a permit nobody closed is a space somebody may still be in. Two rules make the difference in practice: the issuer does not enter, and the permit is cancelled rather than extended when anything on it changes, including the weather, a new contractor arriving or a break for lunch that empties the site of the trained rescuer.
What is classed as a confined space, and what the label changes
Classing a space as confined has consequences, which is why the question is asked by people hoping for a no. Once it is one, entry is only lawful where the work cannot be done from outside, a safe system of work is required, and emergency arrangements have to be in place before anybody goes in, which means trained people and equipment on site rather than a phone call. That is why the honest test is applied to the TASK and not to the room, and why over labelling is as unhelpful as under labelling: a business that calls every plant room a confined space ends up with a procedure nobody follows, and the day a real one comes along the controls have already been devalued. Where the answer is genuinely borderline, write down the reasoning and the specified risk you considered, because that record is what an inspector reads rather than the conclusion on its own.
Questions people ask about working in confined spaces regulations
Is a permit always required?
Not by name in the regulations, but a permit is how almost every organisation evidences the safe system, and for anything beyond the simplest low risk entry a client or principal contractor will require one. What the regulations require is the safe system itself and the emergency arrangements. The permit's value is that it forces the checks into an order and records who authorised the entry, which is exactly what is examined afterwards.
Who can carry out the rescue?
Somebody trained and equipped for that space, on site, before entry begins, and not the fire service as the primary plan. Relying on a 999 call is not an emergency arrangement: the response time is longer than the time a person has in an oxygen deficient atmosphere, and the fire service may reasonably decline an entry they have no information about. For higher risk entries that means a standby rescue team; for medium risk it usually means retrieval from outside with a tripod and winch, which is why the retrieval line is clipped on before the operative goes in.
Does this apply to a domestic cellar or a loft?
Only if one of the specified risks is reasonably foreseeable, which in an ordinary loft it is not. A cellar can become one: a pub cellar with carbon dioxide or a basement being worked on with a petrol cutter both introduce an atmospheric risk that the space's enclosed nature makes dangerous. The test is always the same two part question, is the space enclosed and is a specified risk foreseeable, and the answer can change with the work being done in it.