By RYAN TAYLOR
The family of a young builder killed when a canister of expanding foam exploded as he held it in his hands are still waiting to hear conclusive evidence as to why he died, although they were told in court this week that he had not been to blame for what happened.
James Thomson, 26, lost his life after he was hit in the chest and abdomen by an aerosol can of Evo-Stik foam – commonly used in the construction industry – as he helped build a house in Levenwick with his father’s firm, Dennis Thomson Builders, on 10th March 2007.
A fatal accident inquiry at Lerwick Sheriff Court, which resumed this week after five months, has heard that Mr Thomson staggered out of a room after being hit by the exploding canister as he prepared to apply the foam to windows within the near-completed house. He pleaded for help before falling unconscious on the floor. He died a short time later.
The reason for the long delay was to allow representatives from Swiss manufacturer Polypag AG which produces the canister for Bostik – owners of the Evo-Stik brand – should be invited to give evidence at the inquiry.
Following Mr Thomson’s death it had been assumed he had overheated the foam filler using a fan heater or even a blow torch. However new information brought before the inquiry raised questions over the safety of the canisters – questions only Polypag could provide answers for.
In the end, no-one from the company attended in person. However, on Monday the company’s quality manager Juerg Eugster and chemical technician Torsten Kellner answered questions via video link from Switzerland.
Speaking with the aid of an interpreter, they defended Polypag’s manufacturing process, and said the can that killed Mr Thomson must have been exposed to a heating source of over 90 degrees C.
However the inquiry also heard evidence from witnesses who said a small quantity of water could have entered the canister, leading to a chemical reaction which could have led to the explosion.
One witness thought a manufacturing defect was the most likely explanation for the accident.
Scientists from the Health and Safety Executive disputed evidence from Polypag over how the contents of an Evo-Stik canister could react with each other to cause an explosion.
Making his final submission yesterday, procurator fiscal Duncan MacKenzie said the evidence available was not enough to tell exactly how Mr Thomson died.
“I would submit the evidence can only take us to a point some distance short of providing a definitive answer to that all important question.”
Talking about the canister involved in the accident, he said: “Internal over-pressurisation occurred as a result of an increase in temperature of the can and its contents – the temperature increase being facilitated by an unattributable mechanical or chemical means at some point prior to 10th March 2007.”
Adding his thanks to the Thomson family for their patience during the inquiry, he assured them Mr Thomson had not himself been to blame for the accident that claimed his life.
“James Thomson was not the author of his own misfortune,” he said.
The court had to wait longer than it would have liked to hear evidence from Polypag representatives.
Not only was the whole inquiry put on hold for five months to allow the company to prepare to give evidence, it took over an hour on Monday morning for the sophisticated video satellite link to be set up satisfactorily.
Mr Eugster said the canisters comprised a mixture of chemicals and gases. He told the court Polypag produced up to 20 million cans of foam filler from its Swiss factory with four production lines every year, adding “one hundred per cent” of cans were tested for leakage.
The court heard a “burst test” was also carried out on one out of every 2,000 cans produced, which would involve testing the cans to destruction.
A burst pressure has to be set at 21.6 bar. The court heard a canister bursting below that level would not pass manufacturing standards.
Mr Eugster said Polypag had carried out its own investigation as to why the canister used by Mr Thomson may have exploded.
He said Mr Kellner had carried out a test with a “heat blower” which had destroyed one of the company’s own canisters.
The court heard the tests carried out by Mr Kellner – a chemical technician who specialises in research and development of aerosol packaging – had found a cannister had exploded at 93 degrees C after being immersed in water.
For safety reasons the experiment was carried out with two wooden pallets over the canister, which were weighed down by 50 kilo weights. Such was the force of the explosion, however, it blew through the pallets completely.
He concluded the can used by Mr Thomson had exploded because it had been pressurised after overheating.
The court heard Polypag had carried out only one test with a canister in water and two phases of another hot air test.
The inquiry was told the company had failed to demonstrate repeatability in its tests, which failed to add weight to its evidence.
One of the tests found directing a heat source towards the upper third part of a canister – housing the area where the gas is contained – would cause the heat to transfer down and react with the chemicals in the lower half of the canister, which would in turn lead to an explosion.
Labelling on the product specifically states the canister should not be subjected to temperatures above 50 degrees C.
Mr Eugster denied a suggestion from Mr MacKenzie that water could have entered the canister used in the fatal accident, adding there would be an instant chemical reaction inside the can if it did so.
“When you have filled in everything, including the propellant, the canister is closed by a valve and there is no possibility for water to enter it.”
The court heard the production lines were not exclusive to Bostik, and other products using different kinds of formulation were also built at the plant.
Mr Eugster said pipes had to be cleaned and the manufacturing system had to be informed if one production run came to an end and another was due to start.
Probed further by Chris Dowle, acting for Mr Thomson’s father, Mr Eugster denied there was a danger of overfilling the can with gas or foam as it travelled on the production line.
“The production line makes 35 cans a minute and if there was a mistake it would be in more than one can.”
Health and Safety Executive
On Tuesday, scientists from the Health and Safety Executive admitted they had struggled to come to any conclusion as to how the accident may have occurred.
However Derbyshire-based senior scientist Dr John White said there was a possibility a small amount of water could have entered the canister at some point during the production phase.
He said he disagreed with Polypag’s view it would have caused an instant reaction in the factory, adding the affected can may have made it up to Shetland before the water mixed with the chemicals causing an explosive reaction.
But he remained determined that if water did enter the can, it would have had to have done so during the production phase.
“I think that’s the only time you could talk about water getting into the can,” he said.
Asked if he thought it was possible, or probable, that water had entered the can he said it was only “a possibility – I wouldn’t put it any higher than that”.
On hearing other cans at the scene of the accident had been close to failure because their tops had “popped up” after apparently suffering from high pressure, he modified his view again.
“I would say that makes it more unlikely,” he said.
Asked by Mr MacKenzie if he disagreed with Mr Kellner’s view that water would lead to an instant reaction he said: “Yes, I do. That’s not what happens in my experience.”
He also disputed claims by Polypag the transfer of heat from the top part of a canister to the bottom part could lead to a build up of pressure and subsequent explosion, claiming he thought it would work the other way round.
His colleague, metals specialist Janet Joal, told the court that she and gasses, dusts and vapour specialist Darrell Bennet had carried out repeated tests on cans to destruction in a bid to replicate what had happened with the can on the day of the accident.
She said there had been no variation in the micro structure and hardness of the cans they examined.
Clearly frustrated, she said she was unable to find any “conclusive” reason why the Evo-Stik can had failed at all.
“It didn’t matter what we tried. We could never reproduce the accident.”
Mr Bennet said he had carried out a series of tests using a heater similar to the one found in the Levenwick house at the time of Mr Thomson’s death.
Initially heating cans up to 36 degrees C, he went on to heat them to 84 degrees C with a fan heater placed closer to the canister, although at that level the heater’s standard cut off device had been activated.
His tests also established that a sound can would tolerate temperatures of up to 120 degrees C, a level far too hot for Mr Thomson to physically have held.
Solicitor for Mr Thomson’s widow Karen, Lisa Gregory, said Mr Thomson was wearing a thick fleece on the day of the accident, suggesting it would have been cold on the morning of the accident.
“Looking at Mr Bennet’s report that suggested that a heater with its cut off disabled could heat cans up to 84 degrees – even allowing a 20 degrees ambient pressure, which is more than would have been likely, that still does not take us to 120 degrees that would be necessary to cause the cans to fail.”
On Wednesday, the attention swung back towards Polypag, as chartered engineer and scientist Dr John McCullough cast doubt over the company’s manufacturing process.
Discounting all other theories, he said problems at the factory was the only thing left open to him to consider as a likely cause.
“All manufacturing processes can go wrong. Polypag have a quality assurance system, but I can tell you from experience that quality assurance systems mitigate risk, but they do not eliminate it.”
He admitted there was no “positive evidence of a manufacturing defect”, but at the same time there had been nothing to discount it.
“No matter what I look at I can’t get the factual evidence and the theoretical evidence to come together.”
He said it was impossible for the small fan heater to have caused the explosion, and he criticised a test carried out by Polypag that used an industrial blow heater to warm a canister, which helped create temperatures of up to 210 C degrees.
“You’d never get that off a little blow heater,” he said. “It would not be possible to get the temperature required using this small heater.”
He also scotched claims by Polypag that Mr Thomson would have been exposed to temperatures of up to 90 degrees C before the accident, adding that trying to hold the can at temperatures between 65 degrees C and 85 degrees C would have left him with burn marks in one second.
Dr McCullough said the accident was unlikely to have been caused by Mr Thomson smoking a cigarette.
Yet he admitted his suggestion of manufacturing fault was improbable, not least because of the three other cans at the site showing signs of failure, but he considered it more likely than a hot plate or blow torch.
He also dismissed an under floor heating system which had been installed in the house as being the cause of the accident, adding – if it was on – it would not have been hot enough to lead to the explosion.
Stunned colleague James Sandison told the court he had been working in the house with Mr Thomson in the morning of the accident.
The two had been working in separate rooms when Mr Sandison heard a bang.
He went to investigate what had happened and saw Mr Thomson stagger out of a doorway towards him.
“He said: ‘Jim, help’, and then he collapsed,” he said, adding he lost consciousness almost immediately.
Mr Sandison, a joiner for over 20 years, rushed to the nearby health centre, but on finding it was closed went to a nearby house to summon help.
He called the emergency services with a mobile phone, and rushed back to Mr Thomson to administer mouth to mouth resuscitation.
The inquiry heard Mr Sandison told police the fan heater had been on to heat the cans, which was common practice.
He said it was very unlikely that Mr Thomson had been smoking, adding he would have needed both hands to hold the canister.
The inquiry was adjourned yesterday afternoon until 24th February for Polypag witness Mr Kellner to answer further questions.