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Confined Space Entry

Published: 10th Oct 2004


When considering confined space entry procedure, employers integrate many factors into a plan to ensure the safety of all involved. In the UK under the Confined Spaces Regulations 19972, employers must first try to avoid the need for a confined space entry.

Confined spaces can be found in almost all industry sectors.

However, due to the wide variety of potential hazards faced no two spaces are the same and nor should they be treated as such.

Even with the plethora of confined space entry legislation and the advanced technology available fatal accidents are still occurring. On average there are 15 deaths a year in the UK alone1, making confined space entry a real issue for industry.

When considering confined space entry procedure, employers integrate many factors into a plan to ensure the safety of all involved. In the UK under the Confined Spaces Regulations 19972, employers must first try to avoid the need for a confined space entry. Where this is not possible, employers must:

  • Carry out an assessment of the risks associated with entering a confined space and draw up a safe system of work
  • Limit entry to the confined space to employees who are competent for confined space work and who have received suitable training
  • Verify, prior to entry, that the atmosphere in the confined space is safe to breath; provide any necessary ventilation; and
  • Make sure suitable rescue procedures are in place before entry in to the confined space is permitted. These rescue arrangements should not involve risks to the safety of the people intended to carry out the rescue

Recent incidents, such as the tragic death of three employees who were asphyxiated in a slurry tank in Thetford in the UK3, have highlighted the risks of confined space entry and the need to ensure that correct procedures are always followed.

The education of workers as to what constitutes a confined space and the hazards they may pose is paramount. When considering that the Confined Space Regulations 1997 define confined spaces 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'

a confined space can be found almost anywhere, from a tented enclosure on the side of the road in which work is taking place to the entrance into a petrol tanker to carry out maintenance work. The possible risks associated with confined space entry are vast and specific to each individual situation. Risks can include injury from moving mechanical equipment, extremes of hot and cold, noise, vibration, electricity and radiation exposure. This article will focus on one of the most dangerous areas of confined space entry - hazardous atmospheres.

Hazardous atmospheres

Oxygen deficient atmospheres have a tendency to take priority when assessing the hazards associated with confined space entry and when planning appropriate procedure as individuals can be veryquickly rendered unconscious, with little or no warning. However other atmospheric dangers also need to be thoroughly considered and planned for, including flammable substance, oxygen enrichment and the threat from toxic gases, fumes and vapours.

Along with oxygen related problems danger from gases in the atmosphere, whether toxic or flammable, is faced by confined space entrants as many such gases are colourless, odorless, and can rapidly render an atmosphere life threatening. These hazards not only need to be considered during planning. They need to be monitored prior to entry and continuously throughout the period of time spent enclosed within the confined space.

The need to protect workers from the possible exposure to gases when working in confined spaces has been long acknowledged, even before Sir Humphry Davis produced the original flame safety lamp in 1816. Legislation associated with some terrible accidents and, latterly, massive insurance pay-outs has largely driven the increasing demand for personal safety gas detectors.

It must be said that without extensive research into new and better detection technology, and companies taking a view of continuous improvement with regard to designing and manufacturing portable gas detection instruments, safe working practices would be severely restrained. The real success story is that as a result of commercial research many lives have been saved around the world.

Portable gas detection development

Sir Humphry's flame safety lamp, known as the "Davy Lamp", was not the first portable gas detector but it was the first designed to be safe. The original lamp was manufactured for detection of flammable gases. In actual fact it was designed for the detection of methane found in coalmines. Oxygen deficiency was also considered using the height of the flame as guide. The lamp was also adapted to become a true confined space monitor with a piece of lead acetate paper to detect the presence of hydrogen sulfide. This was not the safest approach, as a user may not always be aware that the paper had turned black and therefore the atmosphere had become deadly.

The Davy Lamp progressively evolved over a hundred or so years, eventually gaining some basic electronics incorporated into its design to operate a battery powered light in order to warn users of the danger of a lack of oxygen or to inform of an excess of flammable gas.

In 1949 an electronic version of the original safety lamp was produced by Mine Safety Appliances Company (MSA) using high power pellistors in a Wheatstone bridge diamond arrangement. Unfortunately the instrument was very power hungry, requiring a massive battery pack (that originally powered the cap lamp). It wasn't until the 1960's that lower power pellistors were developed, making truly portable electronic flammable gas detectors available, originally manufactured by MSA.

It was the invention of oxygen and toxic electrochemical sensors by City Technology in UK and the use of these by then Neotronics Ltd UK in the late 70's that really began the demise of the flame safety lamp in favour of the monitors we see today. Since the introduction of the Neotronics range of personal gas detection instruments many companies have produced similar confined space gas detectors largely based around the same format of three electrochemical sensors for oxygen and toxic gases with a flammable sensor.

Newer instruments and sensors have progressively become smaller, lighter and generally of better quality than the forerunners but otherwise similar to the original package.

It is now considered standard that a typical confined space monitor is intrinsically safe and detects flammable gases, normally using low powered pellistors or IR benches. Combined with electrochemical oxygen, hydrogen sulfide and carbon monoxide sensors, all packaged in one instrument often small enough to fit in the palm of the hand. Creative companies like BW Technologies over the last decade have dramatically driven the costs down and increased the availability of these protection instruments. Workers are safer today than they have ever been, and this trend will certainly continue as long as men and women need to, or are perhaps even permitted to, enter confined spaces.

Whilst this latest range of instruments generally gives adequate protection in the majority of applications of confined space entry, they only concentrate on the main risks and substances that are most likely to cause harm. These being a lack of oxygen due to poor ventilation and reduction due to other gases present such as carbon dioxide, flammable vapors from various sources or leaks of natural or town gas, hydrogen sulfide from decaying matter and carbon monoxide from combustion engines exhaust.

Some manufacturers offer additional electrochemical sensors to cover other specific gases such as chlorine used in water treatment or hydrogen cyanide used in gold extraction.

However in many situations, such as entering live sewers and culverts near roadways or industrial producing factories, these instruments, as good as they are, do not detect the thousands of other potentially toxic volatile compounds that could possibly be present. Therefore the risks to workers in these areas are certainly higher when considering all their health and safety needs.

Volatile Organic Compounds or VOCs

A very broad group of potentially hazardous gases are simply known as Volatile Organic Compounds or VOCs. These gases contain at least one carbon atom, they easily vaporise at room temperature, have no colour, smell or taste and therefore are difficult to detect. VOCs include a wide range of compounds such as benzene, 1,3-butadiene, toluene, methyl acrylate and trichloroethene. VOCs can be found in everyday life and in a wide range of industries. For example, they can be found in gasoline fumes, paint solvents, air fresheners, dry cleaning fumes, inks, chemical manufacturing and synthetic fibres.

Although volatile organic compounds are not always immediately dangerous to health they can cause cumulative permanent damage if exposure, even at very low levels, is prolonged, and at higher concentrations over a short period of time. For example VOCs containing substances such as halogenated or chlorinated solvents and halowaxes can cause severe damage to the liver leading to toxic hepatitis which can in some cases lead to death4.

Other illnesses associated with VOC exposure include heart sensitisation, anesthesia and loss of consciousness, and various forms of irritation to the eyes, respiratory system and skin, including dermatitis. Other VOCs, including benzene for example, are carcinogens (cancer causing) when exposure is sustained over a period of time, and due to these known health risks benzene is being phased out of petrol.

On the extreme end of the spectrum there are a number of VOCs which have been taken and used as weapons, such as mustard gas, arsine and Sarin. Although VOCs of such high toxicity are not commonly encountered in the work place, they present a real concern to police forces and specialist emergency response teams. These teams are involved in searching for chemical agents which have a tendency to be concealed in confined spaces.

At the other end of the scale there are a host of VOCs which can be attributed to workplace illness such as simple skin irritations or rashes and whilst they may heal they do mean a considerable number of days off, in some cases whilst this process takes place. According to the Health and Safety Executive in the UK between 2000 and 2002 an estimated 40 million working days were lost: 33 million due to work related ill health and 7 million due to workplace injury5.

As well as the obvious inconvenience and distress to workers, the total cost to business due to these absences is vast and anything that can reduce these figures will be welcomed by both employees and employers alike.

As nasty and dangerous as these vapors are, they cannot be adequately protected against by a standard confined space monitor containing a pellistor for flammable gas detection and electrochemical sensors for carbon monoxide, hydrogen sulfide and oxygen, at hazardous thresholds. These gases and vapours, which are potentially dangerous at very low ppm or even ppb levels, are part of such an exhaustive list that a confined space monitor with a separate sensor for each would be impossible to make - that is allowing for the fact that it needs to be portable as well as affordable!

Photo-Ionisation detectors

The solution for these types of confined space entry applications where it is possible that VOCs may be present is to use a high quality photo-ionisation detector (PID). For those readers who are unfamiliar with PID technology it operates by passing the gas drawn from the atmosphere over the face of a UV lamp window, which is emitting light particles (photons) of high UV energy. This is where photoionisation occurs: light effectively ruptures VOC gas molecules creating separately charged ions, one positively charged and one negatively charged.

The electrodes within the instrument attract the ions towards them where they are neutralised, generating a photoionisation current that is proportional to the concentration of the molecules present, allowing the signal to be amplified and displayed as a gas concentration. The gas then recombines and passes out of an exhaust in the instrument back into the environment.

There are a number of successful manufacturers who currently produce PID instruments of various qualities, detection levels and with differing capabilities. All manufacturers utilise PID technology as described above using a UV lamp but with varying modifications and design differences, for example, to allow for higher sensitivity and humidity compensation.

The top brands manufacturing these detectors ensure their instruments are capable of resolving to ppb (parts per billion) levels where many gases are dangerous to health, coupled with a massive dynamic range and an incredibly fast and reliable response (typically T90 <1 second), giving their customers the confidence that there employees have the safest coverage of even the most unpleasant gases and vapors. The added advantage with these non-specific detectors is the wide range of gases that they are capable of detecting.

Although PID is non-specific, a number of brands offer an exhaustive gas table built into the instrument so that should a user know the VOC present they are able to ensure accurate and reliable readings for that extra peace of mind. However it is the broad range that makes these detectors invaluable in confined space VOC measurement.

PID was originally developed by Dr. James Lovelock of Cambridge University, UK in the 1960s as a highly sensitive laboratory analytic gas chromatography technique. In the past the technology was only really utilised in portable instruments by companies who simply copied the original invention, with very little improvement upon the original idea. However in recent times PID has been refined by Ion Science who have also further adapted the technique for part per billion (ppb) sensitivity for most VOCs. With a dynamic detection range from 1 ppb to 10,000 ppm it makes the technology one of the most sensitive to VOCs available worldwide.

Other PID manufacturers include Rae Systems, Industrial Scientific, Photovac, Thermo and HNU, all of the US, offering detection capabilities that give the customer a wide choice of instruments to choose from to find an instrument that best meets their specific detection needs.

Many companies, conscious of the potential risks to their workers beyond normal confined space issues posed by VOCs, are purchasing these separate PID devices to complement their existing confined space instruments to add to the precaution in these areas. Some of these companies with high risk of VOC gases make it mandatory that they use a PID instrument throughout their whole plant.

The next generation of combined instruments

Confined spaces are exactly that - they have a tendency to be small in size and in many cases workers have a large amount of equipment upon their person when entering these spaces. To carry one traditional confined space instrument is acceptable but to carry an additional instrument, and in most manufacturers cases two instruments in order to cover ppb levels, to ensure protection from VOCs the entrant is fast becoming swamped with devices. Although these instruments are necessary to ensure workers' safety from hazardous gases, to carry three gas detection instruments can be an inconvenience in many applications.

Due to the increasing demand for complete gas detection coverage by companies for the safety of their employees when entering confined spaces gas detection manufacturers have been looking at ways to create a practical and affordable solution to the problem. Both Rae Systems and Ion Science have recently successfully launched combined instruments, which not only contain sensors for the traditional confined space gases (oxygen, hydrogen sulfide, carbon monoxide and explosive gases) but a photoionisation detector to cover the wide range of possible VOCs in one convenient handheld instrument. Now the worker can enter a confined space with the confidence that they are covered for the traditional confined space gas hazards as well the dangers posed by other toxic gases which may be present.


Confined space entry should always be avoided wherever possible. However, some instances are unavoidable and can be incredibly dangerous for the workers involved. Depending on the individual situation, employees may face a wide variety of hazards. Adequate detection of hazardous atmospheres within a confined space is paramount when considering the safety of entrants from immediate danger, and as gas technology continually improves our ability to protect workers from more long term damage from toxins such as volatile organic compounds is possible. With the huge choice of gas detection equipment available and with the advent of the combined traditional multigas instruments with PID technology it is safe to say that workers are safer today than ever before.


1 Safe Working in Confined Spaces; published by the Health and Safety Executive, first published 10/97.

2 The Confined Spaces Regulations 1997. A copy of the legislation can be accessed via the HSE website




Published: 10th Oct 2004 in Health and Safety International

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