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HOTWORKS & HYDROGEN In response to the story in our last issue is story on hotworks, Tom Clunie of Whangarei and Neil Dobbs of Work Injury Care Ltd warn readers of the hidden danger of hydrogen O n reading the article 'Fire Below' Professional Skipper July/August, I would like other readers to beware that not all potential explosions are from hydrocarbons gas build-ups, especially in voids of aluminium constructed vessels. I myself have had the unpleasurable experience of blowing up a boat. It just happened to be my own, an almost new 4.5 metre Lazercraft. This occurred when I attempted to change my fish-finder by welding up a 3mm hole in the transom to fit a new transducer. As supervisor within a large ship repair yard, I decided to carry out the replacement in the company workshop after hours. I left the boat outside in the sun all day and around 3pm moved it into one of the main workshops. Prior to starting I removed the bung from the double bottom and two tote tanks which held the only fuel aboard – the boat did not have under floor fuel tanks. On starting welding up the old transducer holes with a Mig Welder there was an almighty explosion. The force of which removed the roof of the workshop six metres above, ripped the engine cover off my 60hp Mariner outboard, just above my head, and caused the boat and trailer to lift about four feet off the ground. Later, one of my screwdrivers was found in a carpark 250m away. My boat was destroyed, with its chine ripped wide open. I was adamant no fuel was present and my job was on the line as the company had rules regarding hotwork on fuel tanks. Luckily for me, the company safety officer investigated the incident in detail and confirmed the explosion was due to hydrogen gas and not hydrocarbons as the local Fire Service were stating. I have asked the now former safety officer Neil Dobbs to comment on my incident and give views based on his 20 years' experience in gas free testing, hazardous substances and workplace safety. When Tom asked me to comment on his incident for Professional Skipper, I jumped at the chance. Why? Because this was so nearly a fatal accident from which we all need to learn. Even then, I thought I was an experienced safety professional but found I had no knowledge that hydrogen gas could be so easily created, nor was I aware of the fact that most hydrocarbon based industrial gas detectors don't detect the risk of hydrogen gas explosions. By leaving his boat in the sun in the carpark, Tom had created all that was required to generate sufficient hydrogen gas to almost destroy a building. This being a void space, condensation, aluminium and a small electrical current – the electric current generated from either the boat battery or the difference between the aluminium plate and welding rod as a mico-cell. The Professional Skipper article focussed on the need to "gas free" test, which I totally endorse, but it failed to highlight hydrogen gas as a hazard despite the fact that I believe that the vessel pictured Blue Heaven was destroyed by such an explosion. www.skipper.co.nz A potentially fatal explosion during hotworks was caused by hydrogen Most gas detectors used to "gas free" voids generally work by taking a sample and comparing it with a known concentration of a hydrocarbon, such as methane (test gas). Such meters will not warn of a likely hydrogen gas explosion unless they are fitted with a specialised sensor specifically for that purpose. If not fitted with a hydrogen sensor the only likely indication that hydrogen gas is present is a very slight increase in oxygen readings, but I can't confirm that at this time. I have become aware of a number of other explosions caused by hydrogen gas like Tom's incident. The explosion regarding the Blue Heaven is a good example and it is interesting that the local Fire Service also incorrectly found the cause to be hydrocarbons. The DOL did produce a "Safety Alert" many years ago regarding the risk of hydrogen gas and aluminium voids, following a very serious injury. After Tom's incident I warned other local aluminium boat builders and was met with some scepticism. One of these sceptics had a brand new boat explode only a few months later. Hydrogen gas, unlike hydrocarbon, is very simple to remove and it does not accumulate during the hotwork process. Hydrogen gas is much lighter than air and will dissipate rapidly if given the chance. This can be achieved by simply opening a hatch on the top of the void or blowing air into a void to remove the air/ hydrogen gas within. The removal of a bung at the bottom of a void is however completely ineffective, as Tom found out. Gas freeing any void before hot work is the best idea but only if it is available with the correct sensors. Can I suggest aluminium boat designers consider building into double bottoms the ability to vent them more easily and warn customers of the risk? Finally, I hope the new government department currently being created to manage Health and Safety in New Zealand industries (formerly OSH) places a greater priority on hazard education and injury prevention. I challenge this organisation to first ask itself what it has done to ensure people have been given knowledge of such risks before prosecuting them in hindsight. September/October 2013 Professional Skipper 39