Effects of fire on small commercial gas cylinders

Current standards on the safety of small portable gas cylinders only define the pressures at temperatures of up to 50 °C and therefore have limited applicability in situations where cylinders are close to fires. Cylinders containing a pressurised liquid butane–propane mixture were heated in a small barbecue. The cylinders underwent a boiling liquid expanding gas explosion (BLEVE) at a liquid temperature of 90–100 °C. Failure was at the rolled seam where gas could escape thus provoking the BLEVE. Previous hydrostatic pressure testing of the cylinders showed that collapse of the spherical cap base occurred at a pressure of 1.8 MPa and that this was followed by failure of the rolled seam at a pressure of 2.0 MPa. These pressures were lower than that required to produce longitudinal cracks in the cylinder wall. Analysis of the pressure created as the temperature is raised by means of the Clausius–Clapeyron equation indicated the temperature for failure of the seam to be about 100 °C. After the BLEVE the cylinder broke into two fragments, an end cap and a tub rocket. The velocity of the tub rocket was estimated to be 65 m s⁻¹, giving a kinetic energy of 309 J. By comparison with the ballistics of rubber bullets it is believed that any injuries will be non-penetrating blunt trauma injuries and be less likely to cause severe injuries than those created by rubber bullets. The range over which the kinetic energy is likely to be capable of creating injuries is estimated to be less than 30 m.