The recent twenty-third technical seminar to be organised by the Institute of Rail Welding focussed, not on technical matters, but safety and welfare. Writes Chris Parker
Mick Downing of Renown Rail Welding Services chaired the day which was entitled “Gas Safety – Risks, Remedies and Requirements” and was held at BOC’s premises in Wolverhampton.
Acetylene cylinders and fire – don’t panic!
The first presentation of the day was possibly the most important presentation. Jointly delivered by Doug Thornton, chief executive of the British Compressed Gases Association (BCGA) and Peter Gustafson of the London Fire Brigade, it concerned the question of the safety of acetylene cylinders when involved in fires.
The BCGA represents the compressed gas industry and has some 78 member companies. One of its major roles is the development and publication of guidance about the handling and use of compressed gases. Some 99 such publications have been issued, all endorsed by the Health and Safety Executive (HSE), and some are even incorporated into UK law, making compliance a legal requirement.
Liaising with regulatory authorities such as the HSE and the Department for Transport, the BCGA works to drive necessary changes in the law. New UK Regulations covering all aspects of Acetylene manufacture, storage, transportation and use will come into force in October 2014 – including an important new provision, making flame arrestors mandatory in oxy-acetylene sets.
Everyone will have heard horror stories about what has happened when acetylene cylinders have been involved in fires. Motorways, stations and railway lines have been closed down because a nearby fire involved acetylene. The infamous example quoted by Doug closed King’s Cross Station for a long period when four acetylene cylinders were in a fire eight storeys above ground on a nearby construction site. Following this event there was even talk of the Mayor of London banning acetylene from the area under his jurisdiction. As a result, the BCGA and the London Fire Brigade co-operated to establish what could be done.
Any gas cylinder will explode if heated sufficiently in a fire. The material of the cylinder weakens as it gets hotter whilst the compressed gas expands and increases the pressure within. Steel cylinders will fail due to this combination of events at around 3000C. Cooling is an effective remedy, as it reverses both the weakening of the cylinder and the increase in gas pressure.
The good news is that gas cylinders are all heat-treated during manufacture so that, if they fail, they do so in a ductile fashion. They do not shatter into pieces throwing “shrapnel” around, but peel apart, releasing their contents relatively gently (though it’s not good to be close when this occurs).
The cause of the fear over acetylene is the process called ‘decomposition’. This refers to the splitting up of the acetylene molecule into solid carbon and hydrogen gas under the influence of heat. Decomposition is exothermic, that is it releases heat as it occurs, in much the same way as burning coal or other fuels in air. The reaction can therefore become self-sustaining once it starts, the heat from the process causing further gas to decompose, releasing yet more heat, and so on.
In addition to the heat, there is a significant increase in the cylinder pressure. The acetylene in cylinders is not held as compressed gas, rather it is dissolved under pressure in a solvent (normally acetone). The solvent is itself locked up in a porous ceramic foam material. The cylinder is therefore under relatively low pressure compared with, say, an oxygen or LPG cylinder.
However, when decomposition creates free hydrogen, this is gaseous. Being subjected to the heat generated during the process, this gas rapidly raises the cylinder pressure. So, whereas for other compressed gases removal of the heat and appropriate cooling removes the risk of explosion, this isn’t necessarily the case with acetylene. Stories abound of acetylene cylinders that have been removed from the heat of a fire exploding hours later without warning, or becoming hot again after being cooled. There have even been claims that physical shocks to hot cylinders have resulted in explosion.
As a result, fire brigades were establishing a 200 metre exclusion zone around any acetylene cylinders and either extinguishing the fire or removing the cylinders from it. The cylinders were then cooled with water for 24 hours whilst being kept under observation, only after which time could they be regarded as safe and the exclusion zone removed.
Temporary hazard zone
The investigations by the BCGA and the London Fire Brigade showed these stories to be inaccurate. Extensive and exhaustive research by reputable international bodies eventually confirmed that, in fact, all that is required is to cool the cylinders for an hour and then keep them under observation for a further hour. Decomposition cannot occur below 3500C and, as it occurs near the cylinder walls, it can be reliably detected by checking the cylinder temperature externally. If by this point there is no sign of the cylinders reheating through decomposition, they are totally safe. This shortened timescale means that creating a long-term exclusion zone is unnecessary.
Explosion due to physical shock alone to a cylinder which has not been fire-exposed was also shown to be impossible. To prove this, tests were even conducted in the USA which involved detonating 90g of plastic explosive attached to a cylinder.
A new fire brigade protocol was introduced in November 2012 and has been a great success. It requires the establishment of a temporary 200 metre hazard zone whilst the situation is assessed, not an exclusion zone. Cylinders should not be moved, but cooled where they lie, for an hour only. After a further hour under observation with no sign of heating by decomposition, they can be treated as safe.
Aside from saving fire brigade resources that can now be better deployed elsewhere, this also avoids the problems caused by the exclusion zones. The King’s Cross incident, for example, caused serious safety problems and delays at nearby London Underground stations due to the crowds of displaced passengers from the main line terminus. At the same time, ambulances had to be diverted from their regular routes. These two examples alone show that there were probably greater risks to society at large from the exclusion policy than there might have been from the potential explosion. Add in the personal and business losses, and it can be seen that the changes of the new protocol will be very beneficial.
Gas equipment testing
Terry Askham of Truflame described the testing of railway gas equipment, referring to the relevant international, national and industry (particularly Network Rail) standards. He looked at the range of equipment used to carry out the CAL 501 tests, from a simple but properly calibrated pressure gauge through to comprehensively equipped test benches as used at his own company facility. Tests include leak tests, pull out tests on connections and axial load tests on flexible hoses, and delegates were shown details of each.
Terry then described the CAL 411 test applicable to Thermit welding pre-heaters, again looking at the test equipment and procedure.
Hazards of compressed gases
Another Terry, in this case Terry Broughton of Gas Safe, gave a thought provoking description of the hazards of compressed gases. He showed examples of typical dangerous situations, acts and equipment, and did his best to frighten everyone into going away to check their own circumstances.
Allowing combustible gas to leak, mixing with air to form an explosive mixture in a confined space, when the necessary spark is all that is needed to cause an explosion, is not a good idea. The potential results were illustrated graphically by Terry’s picture of what was once a mess room and store in a shipping container. Only 2% of gas in air is necessary!
Other bad ideas include oiling threads on gas fittings, failing to treat oxygen with the respect that it deserves as a potential cause of fires, the use of incorrect regulators, the misidentification of gases, the use of incorrect nozzles or other inappropriate equipment, and the use of incorrect gas pressures.
Containers and vehicles used to store or carry gases need sufficient top and bottom ventilation, together with the correct number and type of fire extinguishers. The appropriate gas data sheets should be available and used. Risk assessments and operating procedures should be produced, used and kept up to date. Equipment should be regularly tested and this should be documented. Replacement should be undertaken at recommended intervals.
Staff should be properly trained, equipped with relevant PPE and should know the appropriate emergency procedures.
Terry ended by saying: “Remember, what you permit, you promote”.
Network Rail’s Steve Duffy, Alan Forrester and Isaac Adjei demonstrated how their company is complying with many of Terry’s injunctions by supplying its welders with new vehicles for their work. The seven-tonne IVECO high roof vehicles, one of which was at the conference, are being fitted out by Bri-Star, the first time the two companies have worked together on such a contract.
The original remit was for a vehicle for a three person Thermit welding team, but this is now being adapted to cater for wider welding roles. The plan is to deliver 800 of these vehicles to the company’s teams, about 60 having been made available thus far.
The vehicles are equipped with load indicators which ensure that operators keep below the permitted load limit. Tail lifts are fitted for the safe loading/ unloading of heavy equipment. Network Rail has worked closely with VOSA (Vehicle and Operator Services Agency) over the introduction of these vehicles ensuring that they are registered in the category of ‘Special Vehicles/Engineering Plant’. This puts them outside of the EU regulations on drivers’ hours and operator licensing.
‘Genie’ oxygen cylinders
Piers Capper from hosts BOC introduced the company’s new lightweight ‘Genie’ oxygen cylinders. Using a thin steel cylinder wall reinforced by a carbon fibre wrap, and with a smart, tough HDPE (High-density polyethylene) outer cover, these 20-litre cylinders are 30% lighter than a comparable conventional cylinder and half the weight of a conventional 30-litre ‘BR’ cylinder.
Genie cylinders have digital displays which show both pressure and the quantity of gas remaining (as a percentage of full) and give alarms at 25% and 10% remaining. In July 2014, BOC will be able to fill these cylinders to 300 bar (currently only 230 bar is possible), increasing the quantity of gas that each can carry. It is estimated that whereas four or five welds can be made using the contents of a cylinder charged to 230 bar, the higher fill pressure will increase this to about seven (based on trials completed by Network Rail).
Five Network Rail sites have been using the new cylinders under a trial programme. They have proved very popular due to their reduced weight, good handles and digital displays, and none of the sites apparently wish to return to the old cylinders. There is admittedly some concern that the Genie is less robust than the BR type, and BOC will be keeping a close eye on this. They do consider that the cylinders are likely to be handled more sensitively given their lightness and this should ensure that damage is unlikely.
The seminar closed with an interesting presentation from an organisation called Pristine Condition. Stuart Cruickshank explained that his company specialises in training companies and their staff in how to manually handle loads in a safe way.
The founder of the company was an Olympic weightlifter who became involved when a friend asked for his help. The friend had problems with manual handling injuries amongst his staff, and wondered why weightlifters handling far greater loads appeared not to suffer the same. From this discussion came a company that now has over 3,000 business clients around the world.
Stuart described such things as the importance of the weight of the torso when lifting, and how this weight means that someone may be injured just picking up a light object like a pen. Pristine Condition takes a realistic approach to the problem, engaging directly with the individuals involved. They can train people directly, or train company trainers, and they will produce training DVDs created in the client’s own environment.
They can focus on one activity at a time and train to eliminate the injuries it causes, making a bespoke DVD for each activity in turn. This might be done on the basis of one activity a month, starting with the worst problematic area and working through all in priority order.
Pristine Condition has a “tracker” system that gives managers and supervisors the knowledge to spot poor behaviours themselves and instruct staff in how to improve their technique. They will back up all of this with appropriate support visits to make sure all is going well. They claim unparalleled success with their unique approach to this ubiquitous problem.
Don’t try this at home…
As an aside, Doug Thornton made a brief appeal to people not to get involved, nor permit children to do so, with ‘amusing’ activities with compressed gases. He mentioned helium and carbon dioxide as examples of gases that get abused for fun, and he described the risks attached to things like ‘squeaky voice’ tricks with the former and fogged drinks with carbon dioxide. All very amusing when nothing goes wrong but tragic when someone dies from suffocation or loses their stomach through ingesting liquid gas.