Explosion Prevention: The Normalization of Risk

Vahid Ebadat Ph.D., M.Inst.P, MIET, C.Phys. and Paul Cartwright, BSc, DPhil, CPhys, Stonehouse Process Safety Inc.

To the individual in a processing company, dust explosions don’t happen very often. Indeed, there are very few people who have had direct experience of a dust explosion and its aftermath in their organization. Dust explosions mostly seem to happen in someone else’s company. This observational fact can breed complacency – which is dangerous.

In this article, we discuss explosion prevention through the lens of “risk normalization” – and how to tackle it. We’re going to look at a flour packaging explosion that happened in Switzerland a few years ago, but before we do, we’ll look at what we mean by the “normalization of risk.”

Understanding Risk and its Normalization:

Risk Normalization is:

* The gradual process through which risky/dangerous practices or conditions become acceptable over time.

* Getting used to risky situations because we see them every day.

* Unwittingly accepting unsafe situations because they have not caused an incident before; there has been a lack of “bad outcomes.”

Accepting some level of risk is something that we all do; it’s normal! If we did not accept some risk, we would never drive a car, fly on a plane, or even buy food in a restaurant. But what we have to guard against is over-normalization of risk where consequences of “failure” are big. A combustible dust explosion can, of course, have severe consequences to life, the environment, and your business. But combustible dust explosions are not usually everyday events. Being surrounded by a familiar, seemingly unchanging process plant and equipment, day on day, easily leads to complacency and quite often, the “normalization of risk.”

Breaking the chain of normalization of risk is important and is something that anyone with process safety responsibility should address. It can be done using internal resources, but the danger here is over-familiarization with plant. How many times can the same person study a facility and spot new things? We argue that it often takes “fresh eyes” to truly see hazards that have been blinkered by familiarization, and as process safety consultants at Stonehouse we have encountered this many times. Perhaps it’s heavy dust deposits on the electrical motor that is always there, or the unprotected dust collector located inside the factory workspace. Maybe it’s the nuisance electrostatic discharge you get from a particular powder receiving vessel or the manager using unsuitable, portable, electrical equipment in a classified hazardous area.

At Stonehouse, we are specialist contractors that undertake dust hazards analysis (DHA)/NFPA 652 compliance work. We also perform process safety assessments on a wide range of topics and in many industrial sectors. We have a vested interest here, of course, but we unashamedly challenge you to argue against our view that fresh, expert eyes are invaluable in truly reviewing process safety hazards – and ultimately in challenging a hazardous status quo and avoiding the normalization of risk.

Flour Packaging Explosion

A few years ago, there was a flour mill in Switzerland, complete with its own packaging station (ref. 1). Like many such mills, the plant had been milling and packaging flour for many years. One day, a fire broke out in the wood-built flour sample room on the ground floor of the factory; cause unknown. Open conveyor belts caused the fire to spread quickly from the first to the third floor where flour sacks were temporarily stored. A dust explosion occurred on the third floor with the pressure raising dust on floors, process equipment, and ledges which was ignited by the following flame front, leading to secondary combustible dust explosion. The explosion thus transmitted through a connecting bridge to the main flour packaging area. A huge explosion led to the collapse of the flour storage building. More explosions followed. Fourteen people died and 17 were severely injured. The material damages were in excess of $100 million.

With plants like the one described above, dust deposits sometimes become the norm and thoughts of proper explosion prevention and protection measures are left unrealized. “Flour mills and packaging facilities are dusty places” is often heard in similar situations. “We’ve had open conveyors here forever” is another refrain. “We have our safety officer that checks us out for dangers (ignition sources) regularly.” “We’ve never had an explosion here before.” The danger is clear, yet the risk remains.

It needn’t be like this. Accepting the status quo, as we have said, is the easy course of action. It’s the comfortable thing to do. You may not always be popular at pointing out a potential hazard that may be challenging to fix. So how to break that trend and those trains of thoughts that normalize risk?

It is apparent with the flour explosion described above that sufficient dust explosion prevention and protection measures had not been taken. We would have expected to have found closed conveyors and better closed plant, better use of dust extraction, and dust collectors fitted with proper explosion protection vents. Improved housekeeping would have undoubtedly helped prevent dust on floors, equipment, and ledges being released to fuel a secondary explosion. Ignition source prevention measures could have included things like detectors for belt slip, vibration detection, classification of hazardous areas, and installation of appropriately rated electrical equipment, bonding and grounding, and more. We would also have hoped to see measures to prevent the propagation of explosion from one part of plant to another – perhaps isolation valves, diverters, or better building design. And, of course, we would expect to see explosion protection devices such as explosion relief vents on process plant to ensure that even if an ignition source eventually finds its way onto plant, then any subsequent explosion would be diverted away from people and lead to minimum damage to plant.

Summary

To anyone working on process plant, normalization of risk is a real threat and should be addressed by conducting periodic safety reviews according to recognized standards and methods (e.g. DHA according to NFPA 652). A good, formalized approach to hazard identification and risk assessment can compel the assessor to systematically review all main hazard areas. In our view, safety studies will clearly also benefit by involvement of third parties who can bring additional expertise, experience, independence, and fresh eyes to produce the best safety outcomes. This can help with the normalization of risk problem. We do this at Stonehouse, of course, but if you are part of a large organization, it can also be possible to bring in specialists from other sites in your group.

Vahid Ebadat Ph.D., M.Inst.P, MIET, C.Phys. is CEO of Stonehouse Process Safety Inc. He has worked extensively as a process safety consultant for the chemical, pharmaceutical, food, paper/wood, and other process industries globally for more than 30 years. Paul Cartwright, BSc, DPhil, CPhys is chairman and co-founder of Stonehouse Process Safety Inc. He has worked in the process industries for more than 30 years, largely in the field of process safety. For more information, call 609-455-0001, email [email protected], or visit www.stonehousesafety.com. 

Ref 1: Case description based on an account published by Swiss National Accident Insurance Fund “Dust Explosion Incidents: Their causes, Effects and Prevention” (2005)