Harmful gases have been a threat to human safety for a long time and those working underground to extract minerals initially used canaries, noting that if the birds detected methane, they would stop singing and become distressed. But it was the advent of the industrial revolution where the risks became so acute that steps were taken to protect workers from harm.

With the advent of the industrial revolution and the technological changes it heralded, industry started using new basic materials chiefly iron and steel. New energy sources such as coal, steam, electricity, petroleum along with motive power from steam and internal combustion engines, powered the industrial revolution. Coal was the early fuel of choice which needed to be mined from deep underground in dark confined spaces with risks of harmful gas escaping, causing fatalities from explosions and rock collapse as well as asphyxiations from inhalation of gas or depleted oxygen levels.

Following a number of serious explosions in Northeast England’s coal mines, Humphrey Davy was asked to find a means of lighting coal mines safely. He produced a number of prototype lamps with his final design being a basic lamp with a wire gauze chimney enclosing the lamp flame. The holes in the gauze let light pass through but the gauze itself absorbed the heat. The lamp was safe as the flame could not heat enough flammable gas to cause an explosion, the flame itself would, however, change colour when gas was present. The ‘Davy Lamps’ as they became known, prevented many deaths in coal mines and are often considered the first safety device invented.

Gas Detection Equipment

Over the centuries there have been great strides made in gas detection equipment in order to prevent explosions and asphyxiations. There are many devices currently on the market which can detect the presence of harmful gases, or the reduced levels of oxygen in the atmosphere. Some of these devices may be fixed monitoring alarms, some are tube or probe sampling devices and others are portable devices which alert those carrying or wearing the instrument. Gas detection instruments can be supplied with various types of sensors which vary from single gas detection to multi gas sensor devices which can detect various harmful gases.

The science behind the detection equipment can be daunting and a buyer may be faced with many choices when purchasing equipment, for example, Catalytic Head Detectors, Infrared Absorption Detectors, and Flame Ionisation Detectors to name but a few. This is why it is important to ensure that a Competent Person is involved in the selection, training, deployment and use of gas detection equipment. The manufacturers and distributors can be helpful and those backed by Technical Departments, will often assist buyers in the selection of equipment by undertaking surveys to ensure the correct equipment is selected. They usually also offer training on how to use equipment which is extremely important that those working understand the risks from gases along with the use and limitations of the products.

Different Types of Devices

As outlined above there are many devices currently on the market which can detect the presence of harmful gases. The choice of monitoring and detection equipment will depend on the circumstances and knowledge of possible contaminants, and this will require input and advice from a Competent Person as well as the supplier when selecting equipment. Gas detectors can be fixed, portable or transportable. A fixed detector is permanently installed in a chosen location to provide a continuous monitoring of an area. They are used to give early warnings of leaks of flammable gases or vapors as well as monitoring concentrations in the atmosphere. A portable detector usually refers to a small handheld or body worn device that can be used for testing an atmosphere in a workplace before entry, for tracing leaks on a gas system or to give an early warning of the presence of gases. A transportable detector is equipment that is not intended to be hand carried but can be readily moved from one place to another. One of its main purposes is to monitor an area while a fixed gas detector is undergoing maintenance.

Technology is constantly advancing and in the science of gas detection equipment, this is no different. The internet and technologies such as Bluetooth, Wi-Fi and 5G can bring online connectivity to most electronic devices. In gas monitoring applications, this means detection systems can wirelessly communicate with other devices giving benefits such as real time alerts and maintenance reporting.

“Ensure that a Competent Person is involved in the deployment and use of gas detection equipment.”

Testing, Calibration and Maintenance

There may be occasions when gas detection equipment fails to detect low oxygen levels or the presence of harmful levels of gas and this could be for several reasons, including the fact that equipment will deteriorate over time. This makes testing and calibration of the equipment extremely important to ensure it is working correctly and to not give false readings. For portable devices, when they are switched on you often see the battery and display are working properly, but what about the internal electronics? The gas sensors may be inhibited by dirt, damp or may be reaching the end of their lifespan.

Bump Testing, using small canisters of gas, is a way of ensuring the portable gas detector is working correctly. This method of testing checks that the sensors respond to the target gas and will ensure the alarm is activated. The aim of the bump test is to use a small quantity of gas from a bump test kit and to expose the sensors to a known concentration of the target gas. If the unit is working correctly then this should trigger the alarm. Bump test kits can be purchased from the manufacturers or distributors. While testing is straightforward, those using the kits should receive instruction and training in the correct use.

Fixed gas detection systems with the detection heads installed in the areas where gases could escape are then connected to a control panel fitted in a safe area. The control panel will normally be constantly monitoring the detector heads to ensure they are functioning correctly. Before workers enter a work area, they should check that the control panel is not showing any faults or alarms.

Gas detection equipment should be set to alarm at a level low enough to ensure the health and safety of people but at high enough levels to prevent false alarms. False alarms are most likely to be caused by fluctuations in sensor outputs due to environmental changes (e.g. ambient temperature, pressure, or humidity), sensitivity to other gases or vapors, or sensor drift. If false alarms become a problem, then one option is to use two detectors in what is often called a ’Double Knock’ system so that the alarm level must be registered by both detectors before the alarm activates.

There are two main reasons for the calibration and maintenance of equipment. Firstly, gas detectors often operate in harsh environments such as high/low temperatures, humidity or are exposed to contaminants. Secondly, gas detectors are classed as work equipment under the Provision and Use of Work Equipment Regulations (POWER), and therefore organizations should ensure they are maintained in accordance with manufacturers’ recommendations. When manufacturers calibrate an instrument, it will be certificated to respond to the correct concentrations of gases. To confirm this, they will normally put a calibration date on the instrument and issue a calibration certificate which can be used as evidence during safety or quality audits to demonstrate effective maintenance management.

When to Use Equipment ?

Gas detection equipment is widely used across a number of high-risk industries including mining, oil and gas, utilities, manufacturing, marine transport, construction and emergency services, but is also used in other sectors not always considered as high risk such as laboratory research or agriculture. All gas detection equipment should only be used after a suitable and sufficient risk assessment has been carried out to determine whether gas monitoring is appropriate and whether any additional safety precautions should be taken.

In locations where there is the potential risk of flammable or explosive atmospheres, equipment specifically designed to operate safely in these environments, will be required. The Dangerous Substances and Explosive Atmospheres Regulations (DSEAR), place restrictions on the type of equipment (including gas detection systems) that can be used in areas where explosive atmospheres may occur. Therefore, whether fixed or portable devices are used in such atmospheres, the equipment should be specifically suited. For example, they should be ‘intrinsically safe’ amongst other considerations.

Portable gas detectors can be used actively or passively. Active monitoring is normally conducted using portable, handheld detectors where the user carries the instrument around while monitoring. Passive monitoring is where the instrument is positioned temporarily in one place to monitor the atmosphere such as when working in a sewerage chamber. This temporary installation may be for a period of hours or days. In all cases, the operator should either have bump tested the device initially or switched the gas detector on and noted the readings in a gas-free area before entering a hazardous area. If actively testing an area by walking through it, the operator should hold the detector probe/head in front to determine if it is safe to continue in that direction.

For testing atmospheres of confined spaces, the sample probe/head should be positioned inside the space with the operator remaining outside, where practicable. The operator should monitor a number of points inside the space, using extended probes where necessary, to take into account vapor pockets and stratification.

The Confined Spaces Regulations

Although gas detection equipment is used for a number of industrial applications, it is mostly used to protect those working in Confined Spaces. Access to and working in these environments presents several safety hazards such as the presence of harmful gases or the deficiency in oxygen levels. If these hazards are present when accessing a confined space, then there is a risk of loss of consciousness or asphyxiation caused by gas fumes, vapor, or oxygen deficiency.

‘The Confined Spaces Regulations’ which came into force in January

1998 are not solely focused on protection from harmful gases, but they do feature heavily in The Approved Code of Practice (ACOP L101), prescribing the measures required to protect those entering or working in confined spaces from harmful gases. The Regulations, along with supporting legislation, outlines the key duties including:

• ✤ Ensure the design and construction of confined spaces considers the risks they pose to safety (CDM requirement).
• ✤ Where work or entry to a confined space is unavoidable, implement safe systems of working.
• ✤ Ensure appropriate training is in place for those entering and working in confined spaces.
• ✤ Ensure there are adequate arrangements in place for the rescue of any person in the confined space in the case of an emergency.
• ✤ Ensure there are arrangements for adequate communication between those inside and those outside the confined spaces.
• ✤ PPE and lifting equipment must be regularly inspected and tested where required.
• ✤ As part of the risk assessment and SSOW, consider a Permit to Work System.
• ✤ While the above is only a summary, The Confined Spaces Regulations ACOP includes references to many other Regulations which need to be considered when planning work.

Conclusion

• ✤ So why is gas detection so important for personal safety? Well, it’s one of a few hazards that evades our senses as we can’t see, touch, hear or smell gases (if odorless), therefore, it is critical that we get early warnings for personal safety.
• ✤ Gas detection equipment has come a long way since the invention of the Davy Safety Lamp and many thousands of workers have been saved the horrors of industrial accidents. It’s only by the use of ever-advanced gas detection technologies and much improved safety management that we continue to decrease the potential for workplace injuries and fatalities. This is, in a way, exactly the same principle that those early mining engineers had.
• ✤ Procuring and deploying equipment can be a technical challenge which is why it is important to ensure that Competent Persons are involved in the risk assessment, selection of equipment, training, and use of gas detection equipment. Remember that manufacturers and distributors are often backed by Technical Departments who can guide buyers through the process of selection deployment and training.

Testing, calibration and maintenance is vital if the equipment is going to operate as intended. It is no good purchasing equipment that will not operate as intended in an emergency situation. The cost of calibration and maintenance should be factored into future budgets. Remember, as the equipment will deteriorate over time, the finance department can depreciate the assets and write off the depreciation as a company expense to reduce taxes.

(This "HSE" Published in October 2023 Edition)