June 24th a 112-foot yacht blazed while being parked in a marina and undergoing repairs for several months; being called a welding accident by witnesses, fire began from the lower deck.
Welding accidents, along with damage to vessels, also lead to death of crew so should be addressed from a perspective of crew and precautions they should take to avoid repetition of such incidents.
Firstly, the two most common types of welding are; arc welding and gas welding, with one more process that associates with it: cutting. Gas welding uses Oxyacetylene which is formed by combination of oxygen and acytelene which are fed into the torch and ignited to produce a gas of 3000 degree temperature.
Arc welding is the most used form for commercial work as it produces fast and hard welds. This weld is done with an electrical machine which uses a circuit that produces produces a high current/ low voltage output; parts to be welded are connected to one terminal of the circuit while electrodes are connected to the other. Electrodes are made of the same composition of metal that material to be welded is made of. Upon contact and slow withdrawal of the electrode to the material an electric arc is formed with a temperature 5500 degrees.
Cutting is the most dangerous form out of the common welds where there is a higher likelihood of fire and explosions where more sparks are produced. Process here is done with similar tools of gas and arc welding.
What is welding fume? It is a mixture of airborne, fine particles which also produce toxic gases upon welding and cutting of substances where 90% of fumes arise from vaporisation on the consumable electrode, wire or rod as material is transferred across the arc or flame.
What are some gases that are encountered during welding and how?
Fuel gases, which form carbon dioxide (CO2) on combustion and carbon monoxide (CO) as the flame reduces. Fuel gases of most heating value from combustion, based on the standard temperature and pressure of – 60oF and 14.73 psi, are Octane, saturated with water, Xylene, Toulene and Naphthalene. Most flammable gas remains Hydrogen. (H2)
Fuel gases carry burn and explosion hazards that have their own precautions and likelihoods and margins of error:
- Care-less handling of the blowtorch
- Welding too close to combustive material
- Cutting open or welding containers with flammables in attempts to repair
- Misuse of oxygen
- Gas Leakages from hoses and valves
- Backfires and flashbacks where the former is when the flame burns back into the blowtorch and happens when the pipe is held too close to the workpiece. The latter is caused by a reverse flow of oxygen back to the pipe , burning backwards.
- Preventing Backfire damage can be done by first shutting off blowpipe valves starting from oxygen and ending with fuel gas. Then shutting off oxygen and fuel gas cylinder valves and cool the blowpipe with water.
- Preventing Flashback damage can be done by a proper light-up procedure by purging the hoses before lighting the blowpipe; use a spark igniter fast after turning it on. Fit the blowpipe with spring-loaded non-return valves which prevent backflow of gases. Moderate pressure of gases and use appropriate nozzles. (Acetylene pressure should NOT exceed 0.62 bar/9 psi)
- Acetylene containers that were involved in a flashback also tend to decompose and thus will explode in minutes where signs of this are container vibration and heating up.
So far it is seen that welding accidents can happen due to many reasons that involve either equipment faults, lack of proper disposal, sparks that fly while welding goes on. High working temperatures that are present alongside dangerous, flammable gases are likely to cause fire in the welding environment. However this type of accident is less common than something like yacht collisions.
Such accidents are random in nature and occur constantly but how to contain and even prevent such issues? We have seen that works such as welding impact environment that surrounds the worker which lead to explosions, fires and other consequences. When the environment is the factor it should be considered and analysed as lives of workers and vessels depends on the overseer’s knowledge on where to place assignments altogether.