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Flange guards – their use and applicability in managing hazardous area zoning

Author : Carolyn Nicholls, RAS Limited

01 July 2022

Numerous different motivations exist for the installation of flange guards on systems containing hazardous substances. The overall effectiveness and benefits of doing so is often, understandably, questioned.

Image: Shutterstock
Image: Shutterstock

(Click here to see article in digital edition)

Here, we explore some of the reasons for uncertainties and reservations around the use of flange guards and consider ways in which flange guards can be of true benefit, specifically in managing hazardous area zoning. A key question asked is whether flange guards could remove the need for hazardous area zoning in certain plant areas.

What are flange guards and why are they used?

Although widely used across industry, it is worth briefly defining flange guards here to set a clear context. Pipe safety shields, also known as flange guards, are used in a variety of industries where their primary application is the prevention of harmful spray-outs and mist formation from failing pipe joints. Whilst such sprays and mists are not limited purely to flammable substances and could also involve toxic, corrosive, and other dangerous liquids such as acids or steam, the focus here is on flammable substances.

Flange guards are not designed to contain leaks indefinitely, but to prevent harmful sprays which could result in harm from fire or explosions, considerable plant down time and capital expenditure. For materials that are only combustible if a mist forms, there is obvious benefit in the use of a flange guard in limiting the extent of a spray and associated mist formation. This raises the question, if a flange guard avoids the spray, is the hazardous zone removed? It is worth noting that this question is not relevant for lower flash point liquids, for example gasoline, which would not require a mist-forming spray to generate a flammable atmosphere at ambient temperatures.

The role of flange guards in hazardous area prevention

The core focus here is the benefit of flange guards in the context of Hazardous Area Classification (HAC), specifically in the assessment of the probability and likely duration of flammable atmospheres. HAC aids decisions as to whether electrical and other equipment needs special protective features in order to prevent fire or explosion.

Image: Shutterstock
Image: Shutterstock

The three levels of hazardous area zoning are defined based on the likelihood of flammable atmospheres being present and for how long:

- Zone 0: An area in which an explosive gas atmosphere is present continuously or for long periods. (>1000h/yr)

- Zone 1: An area in which an explosive gas atmosphere is likely to occur in normal operation. (>10h/yr, <1000h/yr)

- Zone 2: An area in which an explosive gas atmosphere is not likely to occur in normal operation and, if it occurs, will only exist for a short time. (<10h/yr)

Therefore, the correct installation of flange guards will influence the likelihood of flammable atmosphere formation. In turn, this could then reduce the extents of zoned areas. However, it is worth acknowledging that the majority of sites with effective inspection and maintenance procedures will already be placed within the lowest zone, ultimately meaning that the hazardous zones remain the same.

Flange guards are therefore an effective measure in demonstrating that the risk is As Low As Reasonably Practicable, since they will reduce the likelihood of a spray and therefore show that steps are being taken to minimise risk. Crucially though, this only holds true if risk reduction measures such as flange guards are implemented and inspected correctly. Yet, they will not remove the need for a hazardous zone completely since they can still fail and flammable atmospheres could still form even in their presence.

Can flange guards remove the need for hazardous area zoning?

Although flange guards can significantly reduce the chance and extent of a flamamble zone, it is argued that they won’t remove the requirement for zoning as they are not fixed measures, and might be defeated for example due to potential failure to replace them following maintenance. There is currently no guidance from the UK Health & Safety Executive (HSE) or from industry bodies on the use of flange guards for controlling hazardous area classification requirements. So, we wouldn’t suggest their use can result in the removal of zones. Flange guards could however be a good intermediate measure while equipment is being replaced, and are certainly a worthwhile consideration from an ALARP perspective. Rather than totally eliminating the need for hazardous area zoning, the installation of flange guards is believed to lower the frequency at which hazardous zones occur.

Carolyn Nicholls, RAS Limited
Carolyn Nicholls, RAS Limited

If we were to adopt a position where flange guards were used to argue that a hazardous area zone was removed, flange guards would need to be regarded as safety critical equipment with appropriate inspection and maintenance procedures to ensure integrity.

It is unclear whether there needs to be more regulation in terms of functionality testing and maintenance to ensure testing is carried out across the board to a consistent level so that guards are having the intended impact. After all, replacing or installing a flange guard incorrectly could be equivalent to not having it there at all, still allowing spray and mist formation. Development of standards or guidance may be necessary to achieve this. In addition to further regulation on testing, it would seem sensible for there to be standards available for the design of flange guards to ensure they are fit for purpose. Depending on the specific site, substances held and conditions under which they are handled (i.e. temperature and pressure), different flange guard specifications are available to achieve optimum protection.

Are flange guards worth installing?

Although flange guards may not lower the HAC zone of your site or even remove the need for zoning completely, they can still be of benefit from a safety perspective. So long as a compatible design is chosen, the guards are installed correctly and suitable inspection and maintenance procedures are in place, flange guards will be effective in reducing the extent of a hazardous zone. The proven function of flange guards alongside their relatively low cost makes them a worthy investment for any site operating with relevant substances.

About the author:

Managing Director of RAS Limited, Carolyn Nicholls is an MIChemE Professional Process Safety Engineer, and has been in the risk and hazard management industry for over seventeen years. Carolyn leads the RAS team of risk and hazard management consultants and has been instrumental in creating the company’s assessment methodologies. Carolyn has experience of working with a large number of UK COMAH sites to develop safety reports, perform hazardous area classification and provide support in all aspects of risk management, in particular consequence analysis and risk assessment, and evaluating the economic impact of improvement measures.


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