Gas Detection and its Role in Functional Safety

IGD are often asked by prospective clients if it’s necessary to have a gas detection system and if so how does it fit into their risk mitigation scheme. Whatever the facility and activities being undertaken, risk assessments will be undertaken to analyze risks and evaluate how to eliminate and minimize them. There are many methods and approaches to do this, and they’re well documented with many standards, guides, codes of practice and courses available.

However, risk assessment and mitigation can still be a minefield particularly when your main role is the management of a facility and your background is a completely different discipline. The goal of this article is not to repeat what has already been written by others. For an approach to risk assessment the best starting point is the HSE website which provides sound guidance and best practice. The aim with this article is to consider the role that gas detection plays as part of an overall safety scheme.

Figure. 1

Functional Safety Overview

When thinking about your facility and assessing risks you will consider if processes have to be undertaken and if materials have to be used. If so then control of the process and materials in a safe manner will be of paramount importance. There are three basics to consider as far as gases and vapors are concerned

Flammable Gas Hazards

If the facility uses or could generate flammable gases or vapors, you must consider the amount produced. For flammable gases DSEAR regulations state that no atmosphere should be above 25% of the Lower Explosive Limit where flammable gases or vapors are in use or could exist.

Toxic Gas Hazards

Toxic gases will usually come under COSHH regulations and as such will be listed on the HSE’s document reference EH40. If the material has an EH40 listing then occupational exposure limits will be detailed. Another information source would be the Material Safety Data Sheets, or MSDS, provided by the supplier. Again these will list any exposure limits. Where exposure limits are listed you will need to consider how to show compliance.

Asphyxiant Gas Hazards

Asphyxiants are dealt with a little differently. Here the material is perhaps not flammable or directly toxic but they will reduce oxygen levels if left unchecked in a room. Here the British Compressed Gases Association produce guidance note GN11 which states that no-one should be exposed to an atmosphere with an oxygen level lower than 19.5%. Again you will need to consider how to demonstrate compliance.

Functional Safety Gap and the Role Gas Detection Plays

It is hard to demonstrate compliance if your atmosphere is not being monitored. This is an important area where gas detection plays a vital role.

Whilst considering your obligations one question IGD is continually asked is if industry guidance notes and Approved Codes of Practice need to be adhered to if they are not actual standards or legislative documents. By adopting the advice from an ACOP or Guidance Note you will be doing enough to comply with health and safety law.

If you are prosecuted for breach of health and safety law, and it is proved that you did not follow the relevant provisions of the Code, you will need to show that you have complied with the law in some other way or a Court will find you at fault.

Health and safety law applies to all; there are no special cases for size of company, educational or recreational establishments or sectors.

Figure. 2

So in terms of health and safety when considering risk mitigation then with reference to Fig 1.

If nothing is done about health and safety then you have 100% of the risk you have identified. By control of process to mitigate risk in terms of interlocks, ventilation automated shut off systems and such, the percentage risk will reduce. Safe operating procedures training and PPE will then provide further reduction. After these steps have been undertaken there will be a safety gap which will need to be lowered in order to achieve an acceptable risk level. This is where gas detection fits into the safety scheme to act as a backstop to all the other risk mitigation techniques.

As was stated earlier if your atmosphere isn’t monitored you will not know if you have any issues and you will not be able to alert in response to hazards should other mitigation fail.

Gas detection is never a primary safety method but will act as an overall backup to primary mitigation methods.

Placement and type of detectors will be key to effective monitoring as illustrated in Fig 2. Remember that the detectors are reporting the gas level in their location; these levels may be significantly more dangerous closer to leak sources. The detectors must be calibrated regularly to remain effective. Modern systems can be used to not only alarm but also provide automated reporting for self-checking and event monitoring. Utilizing this data from a system provides an effective means to prove compliance to health and safety legislation.

With IGD’s wealth of experience they can help advice on appropriate systems to help keep your employees and visitors safe.

This information has been sourced, reviewed and adapted from materials provided by International Gas Detectors Ltd.

For more information on this source, please visit International Gas Detectors Ltd.