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Gas Detection

Published: 22nd Apr 2013

ARTICLE CONTINUES BELOW

Gases are a widely used commodity around the world, but many of their properties have the potential to cause harm to both people and the environment if they are not fully mitigated.

In its various forms, it can be flammable, liable to asphyxiate or cause health problems, which means engineers, health and safety professionals and others with a remit for removing or reducing the risk the substance presents must deal with each hazard accordingly. Gas detection techniques and technology have a crucial role to play in the fight to protect a company’s workforce and other assets from damage.

There are good practise methods for preventing unwanted gas release and detecting leaks, as well as ways to protect employees, the public and the environment if the gas escapes into the atmosphere. The Institution of Occupational Safety and Health (IOSH) Hazardous Industries Group encourages organisations to adopt these methods, which are equally as relevant to the UK as they are around the globe.

Harmful gases and their characteristics

The most common gases produced are carbon monoxide, chlorine, hydrogen fluoride, hydrogen sulphide, ammonia and flammable substances. Typically, these gases are found in the production of iron and steel, chemicals and petrochemicals, oil refining, natural gas sourcing, refrigeration and water treatment.

It is important to be able to detect some gases, such as those which are toxic or flammable, more urgently than others. There are a number of factors that affect the need for speed of detection: • Type of gas • Temperature, pressure, quantity and toxicity • Proximity to employees and public • The effectiveness of counteractive measures taken against it • The speed and effectiveness of medical intervention

Certain environments require much more finely tuned methods of detection and protection, as a leak would have much greater ramifications; for example, petrochemical plants carry a high risk of gas leakage, which can lead to explosion or fire that not only damages equipment, but puts lives at serious risk. Meanwhile, nuclear power stations use gases, such as CO2, as coolants to transfer heat to generate steam and to prevent reactors overheating. Any loss of CO2 could reduce the efficiency of heat removal and cause overheating. In both of these situations, gas detectors are used not only to keep the process going, but to keep people safe by detecting any gas releases.

How gas escapes

Any system which uses, generates or contains a gas under pressure can develop leaks. But the significance a leak has on the business’s ability to maintain normal activities will depend on the type of gas being used, its pressure and temperature, any products or reactions generated by the process, where the leak is located, and the quantity of gas that could be released.

The location and sensitivity of a detector will depend on where the gas is likely to escape from and when. Although leaks are the result of a host of issues, the most frequent causes are human error, corrosion, tired or faulty equipment, poor maintenance, or accelerated chemical reactions that increase pressure.

Part of the health and safety process for selecting gas detection often involves gas dispersion modelling, using likely locations where the substance could escape as a template. Varying densities, volumes, and temperatures of the gas are tested, along with differing weather conditions, to find out how the gas cloud is likely to form and disperse in the event of a leak. ‘Hazops’ - hazard and operability studies - also examine a company’s equipment and its operation, to determine the possible points at which gas may be released.

Fatigue of equipment is a big problem, and wear and tear is often related to poor and inadequate maintenance. Failed pipe work, poor piping joints, leaking pumps or valve seals, and vents and drains can become the culprits if they are not kept in good condition.

Some types of gas can also cause issues in enclosed spaces and workers can find themselves in a situation where the atmosphere can’t support breathing, so gas detection will be a part of the risk reduction measures.

Workers can find themselves in a raft of unexpected, harmful situations if they aren’t aware of the gases used, produced, or discharged in the area they work in and by the task they are doing. Anyone working in an enclosed environment needs to be aware of the potential releases they could face.

For example, even a task as seemingly harmless as setting concrete gives off carbon dioxide, which can act as an asphyxiant in the right conditions. Organic food or waste can remove oxygen, producing hydrogen and methane as it decomposes, and process plants like oil refineries can release toxic gases such a Hydrogen Fluoride and flammable hydrocarbons.

Areas of focus

Companies in the more hazardous industries will take a structured review of any risks to plant, people and the environment – that will include gas detection. The key is to ensure defence in depth, with a number of different elements of protection which are proportionate to the level of risk. For example, a small cylinder of CO2 does not need as much inspection and risk control when compared to one that contains 20m3 – this is common sense.

IOSH Hazardous Industries Group suggests organisations consider three main areas if they want to make sure they are protected when using harmful gases: • Process control – to ensure that the presence, pressure, reactions and concentration of any harmful gases are controlled, so that gases do not escape into the environment • Loss prevention – to ensure good design, maintenance, inspection, operation and corrosion prevention are in place, so that gases are contained • Loss preparedness – to put in place good gas detection and process monitoring, so that loss of gas is identified if it occurs, and suitable emergency arrangements, to protect people and the environment

The latter of these dictates that gas detection is essential for workers’ health and safety, and is obviously a key focus for IOSH, because of the organisation’s core aim of protecting people at work.

Getting the right systems

Most gas detection systems can be broken down into two categories – fixed and portable. Historically, the early detection systems for gas were very basic, but the principles remain the same to this day.

For instance, the use of canaries in coal mines was later replaced by Davy Safety Lamps, and these can still be used by any individual wherever they are working.

Portable

Modern electronic personal gas detection monitors sound an alarm when the gas rises to an unacceptable level, allowing an individual to work in a potentially hazardous area. The safe working levels workers can be subject to do vary from country to country, but are well documented in literature. Portable detection is also used to help workers undertaking tasks such as maintenance, where employees might disturb or release gas that should not be freely drifting in that environment. Portable devices are also a useful way of sampling gases, where workers need to measure the quality of the atmosphere.

These portable systems are mainly used to ensure the protection of the wearer, whereas a fixed system is mainly used to protect many employees at one time. They check for weak points in the plant where gas might escape, or detect dangerous leaks that may harm many people on the plant, the local community, and the environment.

Fixed

One of the main advantages of fixed gas detection is that the gas detector will monitor an area constantly, so that the leak is spotted even if an operator is not present full time, the appropriate emergency response regardless.

In terms of where they are placed in a building or process plant, this will depend on whether the gas is heavier or lighter than air. By way of example, everyone is familiar with smoke alarms and carbon monoxide detectors – perhaps the two most common methods of fixed gas detection. There would be little point in locating a smoke alarm at floor level, as smoke rises with the heat of the fire. The same principles apply to gas detection, in that detectors are placed in locations that will allow for the earliest possible warning.

A fixed gas detection system is often the easiest way to detect gas, because building structures can contain it, making it easy to pick up. Certain structures, however, release or allow the gas to escape away from its source, meaning the detection process must be more complex.

Gas detection outside requires many detectors to provide blanket coverage across a wide area. After all, without the restriction of building walls and structures, it can escape in any direction, depending on wind and weather conditions at the time. In these circumstances, they are installed to cover a number of typically predictable sources of leak, such as corrosion hotspots or sampling points which might get missed by human error.

To be effective, equipment must be able to detect the gas at the concentration required to maintain control or safe conditions. For example, there is very little point in using a gas detection device that will only detect flammable gas when it enters the Upper Limit of Flammability. In this situation, it will have already exceeded the lower limit of flammability and may have already caused a fire or explosion. The sensitivity of the gas detection device must reflect a substance’s lower explosive limit or toxic levels, to give early warning of any danger. Over the years, the acceptable exposure limits have been reducing, either for safety or environmental reasons.

A robust, organisation-wide policy

The nature of the hazardous industries is such that the board is likely to ratify health and safety decisions. The board will view safety reports that have been compiled by multidisciplinary experts, who will set out potential major hazard events that could occur within the organisation, assessing their impact and the ways to mitigate them. These reports serve as a framework for the company to put equipment and procedures in place to help reduce the risks.

Most Hazardous Industries will utilise ‘Hazan’ (Hazard Analysis) and ‘Hazop’ (Hazard and Operability) studies to identify risks with process plant and operations. The results from these studies tell a business what level and standards of gas detection are required to keep their, plant, people and the environment safe.

Detection failures – lessons

There have been numerous fatalities from failures to detect gas and minimise its harmful effects.

In the past, there have been incidents where CO2 has caused asphyxiation to workers, where the gas was released into an enclosed space, or where personnel have entered vessels with an atmosphere that can’t support breathing. While it is very unusual for fatalities to be caused by leaks of asphyxiating or toxics gases, leaks of flammable gases have led to explosions and fires that have caused large loss of life and extensive damage to infrastructure.

The most recent tragedy is Deepwater Horizon, where a blowout from a natural gas leak in the Gulf of Mexico, in May 2010, caused a fatal explosion and fire, killing 11 people. In 2005, 15 were killed and around 170 injured at Texas City when a cold vent system allowed oil production hydrocarbons to be released into the atmosphere, which ignited.

Meanwhile, in the UK, in 1988, the Piper Alpha disaster claimed the lives of 127 people when a leak of natural gas ignited, causing damage to fire protection and secondary fires on an offshore platform. This remains the worst offshore gas incident in history and the resulting legislation, proposed by Lord Cullen in his post-tragedy enquiry, reshaped the offshore industry. All of his findings have now been implemented, or at the very least considered, across the whole of the offshore oil and gas industry.

What makes these events more tragic is the fact that each was preventable – the hazards that could result from the gases released were well known and documented. What is more, the technologies to prevent these accidents from happening were and still are available. Organisations – in the hazardous industries specifically – need to learn these lessons to prevent gas releases in the future, putting in place the right measures to detect them and control them if a leak occurs.

The role of IOSH

IOSH Hazardous Industries Group has risen to the challenge by spreading learning and good practise across all the major hazard industries. One of the ways it hopes to improve knowledge of gas detection is through its cross-sector Process Safety Peer Review Process project.

Process safety is the avoidance of low frequency, but high consequence incidents. It is also known as nuclear safety in the nuclear industry, and as system safety in the transportation industry. But the IOSH project hones in on process safety, covering gas detection and the underpinning principles of process control, loss prevention and loss preparedness.

Process Safety Peer Review differs from safety auditing in three ways. Firstly, it is conducted by functional experts such as control room supervisors, maintenance managers, or design managers, rather than by generalist auditors. Secondly, the functional specialists from separate facilities review and contrast each others’ operations, and thirdly, it focuses on identifying and sharing best practises, rather than finding non compliances.

Following the success of two pilots carried out by the Institution, a two day IOSH course has been created to give candidates a practical understanding of the tools and techniques needed to participate effectively in a process safety peer review.

With the important role gas detection techniques play in process safety, having companies share their policies and procedures from differing sectors could play an important part in raising standards. After all, learning best practise and inputting better systems will only help organisations to fine tune their own gas detection policies, making asset loss due to preventable accidents a far less likely outcome of a leak.

Published: 22nd Apr 2013 in Health and Safety International

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Josh Rice is a Chartered Fellow of IOSH. He is Chair of the Institution’s Hazardous Industries Group.
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