Choosing a Gas Detector for Confined Space Entry

Atmospheric hazards are among the most serious risks in confined spaces, and they are often impossible to detect with human senses. Choosing the right confined space gas detector is a key part of a safe system of work. This guide explains what to look for in a confined space monitor, how to match it to your hazards, and how to keep it reliable.

Why confined spaces need gas detection

A confined space is a substantially enclosed place where there is a reasonably foreseeable risk of serious injury from hazardous substances or conditions. Sewers, tanks, silos, vessels, chambers, pits and ducts are typical examples.

The atmosphere in these spaces can change quickly. Oxygen can be depleted or displaced, flammable gases can build up, and toxic gases such as hydrogen sulphide or carbon monoxide can accumulate. The Confined Spaces Regulations 1997 require employers to carry out a risk assessment, and where entry is unavoidable, to establish a safe system of work. For many confined spaces, testing and monitoring the atmosphere is a central part of that system. Our article on the dangers of confined spaces covers the hazards in more detail.

Choosing a confined space gas detector

Start with the risk assessment

The right detector depends on the hazards identified in your risk assessment. For most confined spaces, the standard choice is a 4 gas monitor measuring:

• Oxygen (O2), for deficiency and enrichment

• Flammable gases (LEL)

• Carbon monoxide (CO)

• Hydrogen sulphide (H2S)

If other hazards are possible, such as solvent vapours, ammonia or chlorine, a multi-gas monitor with additional sensors or a PID for VOCs may be needed.

Pumped or diffusion?

Before entry, the atmosphere should be tested from outside the space, at different levels where gases may stratify. This needs a pumped instrument, or a diffusion monitor with a pump accessory, and a suitable length of sampling tube. Once inside, a diffusion monitor worn in the breathing zone provides continuous personal monitoring. Many confined space monitors can do both.

Alarms and usability

A confined space monitor must be impossible to ignore when it alarms. Look for loud audible alarms, bright visual alarms and vibration. Check that the instrument is easy to operate with gloves, robust enough for your environment, and has enough battery life for a full shift.

Records

Datalogging and event logging can help you demonstrate what the atmosphere was during an entry and investigate any alarms afterwards.

Keeping a confined space monitor reliable

A confined space gas detector is only useful if it is working properly. Most manufacturers recommend:

• A bump test before each day's use, to confirm the sensors and alarms respond

• Calibration at least every six months, or more often if your risk assessment or the manufacturer requires it

• Calibration after a failed bump test, exposure to high gas levels, or physical damage

See our article on calibration and bump testing for the difference between the two checks. Users should also be trained to carry out pre-use checks and to know what to do if the monitor alarms.

Buy, hire or calibrate with 7 Solutions

We supply confined space monitors for purchase and offer 1 week hire of a 4-gas confined space monitor for short projects or to cover instruments away for service.

Our manufacturer-trained engineers calibrate and service confined space monitors from Honeywell (BW and RAE), Crowcon, Dräger, MSA, Industrial Scientific, WatchGas, GMI, Oldham and more. Calibration of any 4-gas confined space monitor costs £50 plus VAT, and every instrument comes back with a calibration certificate. Send instruments to our Hampshire service centre in Waltham Chase, Southampton, or arrange an on-site visit; our Northern Service Centre covers the North East and Yorkshire.

Frequently asked questions

What is the best gas detector for confined space entry?

There is no single best model. For most confined spaces, a 4 gas monitor measuring O2, LEL, CO and H2S, with pumped sampling for pre-entry testing, is the standard choice. Your risk assessment should confirm the hazards.

Do I need a pumped gas detector?

If you need to test the atmosphere before anyone enters, yes. A pumped instrument lets you sample from outside the space.

How often should a confined space monitor be bump tested?

Most manufacturers recommend a bump test before each day's use.

Can I hire a confined space monitor?

Yes. We offer weekly hire of 4-gas confined space monitors. See our gas detector hire page.

Get the right confined space monitor

To buy, hire or calibrate a confined space gas detector, call 01489 326031, email info@7solutions.co.uk or book calibration through our customer portal at portal.7solutions.co.uk.