Gas Cylinder Set-Up in a Crowded Booth
A BTEB short-course booth is shared by two trainees. One is gas welding with an oxy-acetylene set; the cylinders stand in a corner, unsecured, with the acetylene regulator showing a delivery pressure of about 1.5 bar. The oxygen cylinder stands next to it, and both are within a metre of a grinding station where a third trainee is working. A hose runs across the walkway to the bench. The acetylene hose has a small split near the torch end, taped over with insulation tape. The instructor walks in and stops all work.
1. List the unsafe conditions in this booth and explain the risk each one creates.
Read the worked answer
- Unsecured cylinders: a knock or fall can shear the valve, and a released acetylene or oxygen cylinder can become a projectile. Cylinders must be upright and chained or strapped.
- Cylinders within a metre of grinding: grinding sparks and hot particles can damage hoses and heat the cylinder. Cylinders should be kept clear of hot work and spark sources.
- Acetylene delivery pressure of about 1.5 bar: free acetylene is unstable above roughly 1 bar (about 15 psi), so this is above the safe working limit for the set. The regulator setting should be reduced to the manufacturer's recommended range, well under 1 bar.
- Split hose taped with insulation tape: the tape is not a pressure-tight or fuel-resistant repair. Acetylene can leak, creating a fire and explosion risk. The hose must be replaced.
- Hose across the walkway: a trip hazard and a route for mechanical damage. Route hoses overhead or along the wall.
- Two trainees sharing a booth without clear separation adds congestion and confusion.
2. Describe the correct sequence for shutting down and making the set safe before any repair is attempted.
Read the worked answer
- Close the acetylene cylinder valve first, then the oxygen cylinder valve. Closing the fuel gas first is the standard order so that any residual oxygen in the torch does not burn back into the fuel line.
- Open the torch valves one at a time to bleed the pressure from the regulators and hoses. Watch the gauge needles fall to zero.
- Once both gauges read zero, back off the regulator pressure-adjusting screws fully.
- Close the torch valves again.
- Disconnect the damaged hose and replace it with a hose of the correct grade for acetylene, fitted with the correct hose fittings and secured with proper hose clips.
- Do not attempt the repair with the cylinders open or with pressure in the line. Only after the set is depressurised and the hose replaced should the set be leak-tested with soap solution and put back into service.
3. The trainee argues that a 1.5 bar acetylene delivery pressure is fine because the torch still lights. Judge this argument and state the correct working pressure approach.
Read the worked answer
The argument is wrong. A torch lighting only shows that gas is flowing; it says nothing about whether the pressure is safe. Acetylene becomes unstable and can decompose explosively above roughly 1 bar, so a 1.5 bar delivery pressure is above the accepted safe limit regardless of how the flame looks. The risk is not visible in the flame.
The correct approach is to set the acetylene regulator to the lowest pressure that gives the required flame, following the manufacturer's recommendation, and to keep it well below 1 bar. The oxygen side is set to suit the work. The trainee should also understand that the regulator setting is a safety limit, not a convenience setting, and that the instructor's stop order was justified.