Adapting Hazard Studies for Extreme Weather

Article by Mike McKay CEng FIChemE and George Watson

The original HAZOP methodology developed by ICI has been expanded over time. Mike McKay and George Watson believe the eight study stages provide the perfect blueprint to identifying potential Natechs

HOW MANY of us ignore extreme weather events as they are invariably “somewhere else” and so don’t affect us? Certainly, that was our response until early 2023 when we were revalidating a hazard study for an oil storage terminal in South Africa.

During the study we discovered that the site had been submerged in 2022 by flood waters up to 1.8 m in depth. This destroyed the site electrical infrastructure as well as damaging many of the plant’s instrumented safeguarding systems. Fortunately, the flooding did not cause any significant spill of oil. But 18 months after the floods, the site is still operating with temporary measures in place to manage the risk. However, other operators have not been so lucky and there are numerous incidents around the world where a major accident hazard has occurred as a direct result of extreme weather.

Many articles have been published describing the threat that extreme weather poses, often under the banner of Natech, or Natural Hazards Triggering Technological Accidents. Several of these articles describe measures that can be implemented to mitigate the effects. However, if our perception remains that extreme weather won’t affect me then nothing will change until it is too late.

While some sectors, such as nuclear, are addressing the threat of extreme weather, the wider chemical industry is lagging. On completion of our study, we asked ourselves, “Could we identify the risks that extreme weather poses through hazard studies?”.


A hazard study 2, or HAZID, is an obvious place to assess threats posed by extreme weather effects. Its purpose is to identify significant hazards, both on-site and off-site, and ensure that there are appropriate measures either to eliminate or reduce the risk to a tolerable level. The study uses guidewords to facilitate discussion. These guidewords can easily be adapted to consider extreme weather events:

  • The impact of extremes of ambient temperature – hot or cold – can be addressed through “extreme temperature”. The effects should not be limited to the process but also to the utility supplies, increased heat stress on plant operators and even the ambient temperatures in control rooms
  • Wildfires became more prevalent during 2023 and should be readily identified through consideration of external fire
  • Structural failure can occur from extreme weather such as flooding, high wind, subsidence, and wave damage. It can also occur through incremental weight increase, eg due to snow loading. Many HAZID guideword lists include “excess loading”, which can be used to prompt consideration of the consequences of structural failure from extreme weather
  • Structural failure can also occur through periods of low/no rainfall lowering the water table, and so undermining the foundations of structures. Again, this can be identified through excess loading
  • Strong winds can cause damage to vulnerable plant through flying objects. Puncture or burst are common guidewords, but these tend to focus on internal causes. When external factors are included, these tend to be a narrow list such as vehicle drive away, vehicle crash, scaffolding, and domino effects. Again, consideration of flying objects can easily be captured through additional prompts against the puncture/burst guideword
  • Flooding is an extreme example of high level! However, the prompts that tend to be associated with high level tend to focus on process (internal) upsets rather than external factors. Consideration of external causes of high level would allow the threat of flooding to be assessed


Article By

Mike McKay CEng FIChemE

Principal process safety consultant at TÜV Rheinland which acquired ownership of ICI’s eight-stage hazard study methodology through a buyout of ABB Consulting

George Watson

Undergraduate at University of Manchester

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