It is just two years since the dust explosion at the Bosley mill in Cheshire occurred in which four people died. Yet experts are still concerned that too many sites and personnel remain unaware of the dangers the phenomenon presents.
Professor Mike Bradley, director of The Wolfson Centre for Bulk Solids Handling Technology, based at the University of Greenwich, says: “The ATEX directive has been mandatory for many years now, but I am surprised at how often I go into a plant where combustible dusts are being handled and processed, and when I ask what they are doing about ATEX the reply I get is something along the lines of ‘what’s that?’”
Two points stand out: firstly, you can’t rely upon outside expertise alone; second, don’t assume that dangers are focused only in areas where machinery is concentrated.
If a mistake is made and an explosion does occur, it will still be the plant owner and not the consultant who will be in the dock
Professor Mike Bradley, director, The Wolfson Centre
“It isn’t good enough for the plant owner to engage a consultant to do his ATEX/DSEAR risk assessment,” explains Bradley.
“He needs to have his managers and workers trained to at least some level in this, not least because the situation in the plant will change from time to time and the importance of all workers understanding why do we do this will help to get buy-in.”
According to Bill Treddenick, operations director at Lorien Engineering Solutions, the first part of establishing a strategy is to look at the expertise available.
“In practice,” explains Treddenick, “most companies look at two out of three options: hire in, train in, or buy in.”
Bradley [pictured] insists that a compliance system is much better if the day-to-day line managers and operators also understand the matters to a sufficient level.
He adds: “I do fear that far too many companies rely on external consultants to help them with their compliance, and I don’t believe that is the right thing to do, because if a mistake is made and an explosion does occur, it will still be the plant owner and not the consultant who will be in the dock.”
ATEX compliance may not be hard to enforce, but does need to be a continuing effort rather than delegated to a consultant.
“You can’t just tick the box and then forget it,” says Bradley, “so I am a firm believer that every company needs to have someone who is trained in the matter and uses their own judgement.”
A useful starting point says Treddenick is to refer to the regulations – with which standards do you need and wish to comply? This can mean considering the requirements of a COMAH site, then whether other codes might apply – CIRIA 736 for example.
A gap study is a good way to determine compliance for an existing plant and can inform further work such as determining the basis of safety and Hazardous Area Classification (together with possible plant re-equipping).
Most companies look at two out of three options: hire in, train in, or buy in
Bill Treddenick, operations director, Lorien Engineering Solutions
If the plant is not yet built, advises Treddenick, management should ask: “has time and resource been planned in, such that the plant design team has access to the correct terms of reference to enable the plant spacing, system design and choice of equipment to be completed to avoid unnecessary cost?”
In order to establish a strategy for hazardous area inspection and maintenance, one of the most important factors is raising awareness amongst management and staff at all levels.
The most critical task is to identify precisely what constitutes a hazardous area. “You can easily have a hazardous zone, but we know from long experience that the biggest danger to life and property arises from dust accumulating in the working environment, on the floor, on top of machinery and beams, lights and so on,” explains Bradley.
“This can support a secondary explosion – in the event that a piece of equipment suffers an explosion internally and bursts or vents, the pressure wave released by this primary explosion travels through the workplace, lifting dust into the air where it is ignited so that a fireball travels through the whole place.”
Massive devastation can arise from the dust deposits outside equipment – on floors, lights and beams. Without the presence of this, an initial explosion could be rendered a very limited event with probably no loss of life, says Bradley.
Hence, any strategy for both inspection and maintenance must include inspection of the whole workplace – not only such obvious areas such as the insides of machinery and silos.
This will also vary from time to time, especially if handling various materials (for example, sugar from different suppliers, that has a different dust content) so inspection needs to be ongoing. The whole workforce needs to be involved in being vigilant about identifying any changes in dust release and prevention or cleaning requirements.
When carrying out ATEX inspections, zoning areas is a priority. Defining a zone entails properly describing the frequency at which you can reasonably expect an explosible concentration of dust in the air.
“It’s not just about having some dust in the air, it’s a high enough concentration to be explosible,” explains Bradley. “That’s a very thick dust cloud, visually, not just a few particles floating in the air.
On the floor, for example, if you have sufficient dust to write your name in, you have the potential for an explosible dust cloud if an event whips it into the air.
In general, anywhere people are working [apart from the immediate vicinity of sack tips] should be kept clean enough to not present a hazard.
Remember too that a given piece of equipment will often have a different zone inside and outside. It’s not sufficient to ascribe a single zone to a piece of equipment and the items in each zone need to be suitably chosen for compliance.
“Inspections must be undertaken by technically competent people who are experienced in undertaking such inspections,” says Treddenick.
The running conditions may be completely different to the at rest conditions, and both states need to be observed.
Inspections must be undertaken by technically competent people who are experienced in undertaking such inspections
“Management may order a complete plant clean-up prior to an inspection to convey an impression of good housekeeping,” explains Treddenick. “This provides the engineer with a false perspective, and they may advise incorrect recommendations.”
Those charged with inspection need to know the potential areas of failure such as exposed wires and incorrect cable glands fitted, missing earth-bonding straps, missing elements in explosion relief systems, and many more common issues.
Any inspection is an act of work, and needs to be risk assessed with the appropriate permit to work process – access to equipment at height, in hazardous zones, or in confined spaces.
Having an external partner who specialises in the area [such as ATEX] often provides an economical and versatile solution. Many organisations take this type of regular training from their external partner as part of an inspection and audit process and to remain in compliance with the law.
In context via ATEX
The ATEX regulation system is simple to use provided one exercises due diligence regarding zoning and equipment choice.
“Maybe due to the nature of work Lorien does, or the customers we have,” explains Treddenick, “we are seeing a growing awareness of ATEX within businesses to which we provide CapEx project design and management services. This includes the food, drink, household and pharmaceutical industries as well as chemical.”
Multi-national businesses are becoming more aware of their corporate responsibilities and they are striving to apply hazardous area management according to international standards.
Challenging though this responsibility may be, Bradley offers a useful reminder: “Most of the big events are caused by dust on the floor.
“While we obviously encourage all those who process combustible materials to take their DSEAR zoning and ATEX equipment specifications seriously, the reality is that if there is one thing above all others that keeps people safe, it is avoiding the accumulation of dust in the workplace.”