In the cutting and welding business, mixing oxygen and acetylene gas must conform to strict procedures to avoid causing it to explode. According to the American Welding Society (AWS), acetylene has an ignition level when mixed with air of between 2.5-81% volume concentration and oxygen levels of over 23% would significantly enhance combustion. In practice, the oxygen to acetylene proportion must be controlled between 1:1 and 1:1.2 for stable combustion of the neutral flame (temperature approximately 3100°C) to minimize the chance of tempering to less than 0.3%. For example, in 2021, an automaker set the oxygen flow rate incorrectly to 1.5 times that of acetylene, and the resulting mixed gas flow rate was more than 15m/s, resulting in a backfire and leading to an explosion, and a direct loss of $1.2 million.
Equipment selection and testing is the most critical link to ensure safety. Oxygen cylinders must be fitted with a stable operating pressure of 14MPa (normal cylinder capacity of 40L), and acetylene cylinders must be limited to 1.6MPa and provided with ISO 5171-approved tempering preventers, which reduce the danger of backflow of gas by 72%. According to the German TUV laboratory test, with the application of 0.8mm diameter acetylene special pressure reducing valve with ±2% adjustment system flow meter precision, the difference of mixed gas concentration can be adjusted within ±0.05%. For example, when a shipyard replaced a weld defect rate of 5.7% with an automated proportional control system, the weld defect rate dropped to 0.9%, saving $480,000 in maintenance a year.
Environmental monitoring is as important as emergency planning. The workplace must be provided with a combustible gas detector to ensure that the oxygen concentration and acetylene concentration are below 23.5% and 0.5% volume fraction, respectively, and the sampling rate is up to 4 times/second. Experiments have shown that with ambient temperature over 35°C, the rate of decomposition of acetylene is 300% greater, at which time the forced cooling system has to be activated. In a 2023 chemical plant leakage accident, since the detection delay of 0.5 seconds led to the concentration of the gas within the region of 5 cubic meters increasing to the explosion level after 3 seconds (2.8% acetylene+27% oxygen), and finally led to dedetonation, the damage radius of shock waves spread up to 15 meters.
Regular maintenance and training of personnel both have the potential to reduce the accident frequency to a great extent. According to OSHA statistics, companies that unify the daily air tightness test (helium mass spectrometry leak detector sensitivity 1×10⁻⁹Pa·m³/s) are capable of maintaining the equipment leakage rate below 0.01ppm. The workers have to be trained specially for 80 hours with focus on emergency cut-off when there is unusual pressure variation, e.g., the acetylene cylinder pressure reducing from 1.55MPa to 0.8MPa. After a Canadian energy firm adopted VR simulation training, misoperation incidents decreased by 67% and the annual insurance cost decreased by $190,000.
With quantitative control of mixing parameters (e.g., flow ±3%, pressure ±5%), smart interlocking devices (response time ≤50ms), and enhanced risk management (quarterly drills), accident rates with oxygen and acetylene gases can be reduced below 0.07 / MMH. According to the International Institute of Welding (IIW), companies that implement the above standards fully can achieve a return on investment in safety of 320%, while extending the life of vital equipment by 12 years (the original value is 8 years).