Dust-up over explosion risks

Take one empty tin can with tight fitting lid. Make small hole in the side near the base and push in a length of tubing. Place small pot of custard powder inside tin and push end of tube into custard. Now place lighted candle in tin, quickly close lid, and blow through other end of tube. FLASH, BANG! Lid flies off as cloud of custard powder ignites and explodes.

The British Interactive Group loves experiments like this. It aims to encourage hands-on science for kids, and has suggestions for lots of other fun ways to play science with food - like passing 240V mains electricity through a pickled gherkin and watching it glow orange (it's the salt, apparently).

But if kids can make custard explode, imagine what bad housekeeping in a food factory could do with powdered bulk food ingredients such as dried milk, coffee, cereals, cocoa, tea, starch, flour, citric acid and sugar. Almost any powdered foodstuff of a chemically organic nature will do. Simply store and handle badly to produce lots of aerated dust, throw in some stray static electricity, a spark from an unprotected electric motor, or the heat from a worn conveyor bearing - and BOOM, you have a recipe for disaster.

However, in theory at least all food factories have been obliged under the Management of Health & Safety At Work Regulations to assess and reduce the risk explosions from gases, vapours and dusts. Now, however, Europe has got in on the act. And that is worrying UK food companies and bulk handling equipment suppliers.

As of July 1 2003, all new food equipment installed in potentially explosive atmospheres has had to conform to ATEX 95. This is the European Union directive on the explosion-proofing of equipment. In the UK ATEX 95 is implemented through the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR).

But the big concern is that from July 1 this year, ATEX extends to existing processing plants - ie equipment in use before 2003. There's quite a lot of old kit in Britain's food factories and the big question for them is: Will their existing bulk handling plant have to meet ATEX 95 specs, or will they have to replace silos, chutes, motors, and bag fillers with ATEX certified versions?

The answer is yes and no. It is yes because under the so-called ATEX 137 workplace directive, to be enforced through DSEAR from July, manufacturers will have to assess their risk of explosions and show that their equipment is safe. If it isn't safe, then it will have to be replaced or modified. For many factories that could mean a hefty shopping bill, particularly since for the first time, the regulations cover mechanical as well as electrical equipment.

But for those companies that have been doing proper risk assessments under the old Management of Health & Safety At Work Regulations, ATEX 137 should mean little or no change for them after July 1. This is because the standards that underpin the ATEX 95 regulations for the explosion protection of equipment aren't new. They are essentially based on existing BSI and German VDI standards. So if your equipment met the relevant standards and was safe yesterday, it will probably be safe tomorrow.

However, according to many bulk handling equipment suppliers, it's a pretty big if. It's a safe bet, they say, that many food companies have not undertaken a competent explosion risk assessment of their processes under the old regulations. So from July 1 this year they could face a whole heap of problems and an extensive (and expensive) shopping list.

Is it safe?

What ATEX 137 means is that from July, Health and Safety Executive (HSE) inspectors can demand to see your factory's Explosion Protection Document. This is the paperwork that proves that you have undertaken a competent assessment of the risk and severity of explosions from gases, vapours and dusts. You must have assessed those areas where explosions could occur and have classified or zoned them according to their size, the severity and likelihood of an explosion, and its persistence.

There must be paperwork to show that the equipment being used is suitable for operation in those zones. And the document must demonstrate what accident and emergency procedures are in place, how you control work in dangerous areas, and what information and training you have provided for workers.

So what sort of impact is ATEX 137 having on Britain's food companies? According to Mal Sharpley, sales manager for storage and silo supplier Portasilo, the larger food companies will be getting ready for the impending legislation. "But the smaller companies are probably blissfully unaware, especially if they bought old, second-hand equipment when they started up. If it was deemed safe then, in theory they can carry on using their existing equipment. But in practice we are finding that this is not the case, there's a lot of reworking needed."

With old silos, for example, you might still have the original design data, says Sharpley. But if you can't find it, or the supplier has gone out of business, then you're faced with doing material thickness tests to assess the silo's design pressure. From that you see whether the vessel needs modifying to prevent explosions. "ATEX is a serious problem for many companies and could cost them a lot of money."

Rob O'Connell, marketing manager with sieves and separators company Russell Finex, reckons fewer than 50% of food companies have heard of ATEX. "It is very rare we find companies that are fully aware of ATEX and who have done their risk assessment and zoning."

And even where companies do understand ATEX, they seem to be playing safe and are 'overzoning' their factories, says O'Connell. "We are seeing cases of overzoning where companies are rating everywhere zone 20 -- the highest risk. They then buy equipment that matches that rating, which is expensive."

ATEX 137 (ie DSEAR) recognises three zones for dust and vapour explosions. For dusts, zone 20 is the highest risk zone where an explosive cloud of combustible dust is present continuously, frequently, or for long periods. Zone 21 is where an explosive atmosphere is likely to occur occasionally in normal operation. And Zone 22 is the least risky -- an explosive dust is not likely to occur in normal operation and doesn't last long. For gas and vapours the corresponding zones are 0,1, and 2. Under ATEX, new equipment has to be certified for use in a specific zone.

But according to Steve Land, food sector manager for automation company Festo, there is a lack of understanding about zoning for dusty food environments. And bulk bag systems specialist Spiroflow has become so concerned about overzoning that it has produced its own guidance on ATEX. "We recognised that customers were overzoning hazardous areas to err on the side of caution. But there can be severe cost implications for equipment meeting the requirements of zones 20 and 21," says Keith Simpson, marketing manager.

Declan Barry, md of explosion prevention equipment supplier ATEX Explosion Hazards, says there's a lot of old equipment in the food industry. "Most of it will be OK, it just needs to be risk assessed. And that means a shopping list. But if you have got your paperwork in place by July, have a shopping list and can show you are doing something, then the HSE will probably be happy enough."

Identifying hazards

Most food companies will recognise whether they are handling a flammable liquid or a flammable dust from the material safety data sheet (MSDS) for that ingredient, says David Mairs, engineering manager at project management company Projen. However, food companies are fairly ignorant of the standards for equipment protection, he adds. "If the HSE decided to crack down I think they would find a lot of non-compliance." FM