Presentation on theme: "Gas Explosions Ireland Chapter IAAI By Jamie Novak Saint Paul Fire and Safety services Novak Investigations."— Presentation transcript:
Gas Explosions Ireland Chapter IAAI By Jamie Novak Saint Paul Fire and Safety services Novak Investigations
Properties of natural and Propane gas Natural gas LEL lower explosion limit 5%-45,000pp Natural gas UEL upper explosion limit 15%100,000ppm Propane gas LEL 2.15% 22,500 ppm Propane gas UEL 9.60% 95,000 ppm Vapor density -Natural gas 0.6 -Propane 1.5 Ignition Temp Natural gas –900-1170 Propane-920-1120 Heating Value –BTU/FT3-Nat-1000 Propane-2488
Odorant Mercaptans are generally used to odorize fuel gases Natural and propane are to be odorized so they can be detected at 20% of the lower explosive limit. 1.4 lbs per 10,000 gallons
Odorant Since ethyl mercaptan does not vaporize as readily as propane, the concentration of odorant in a propane tank may increase as the tank is depleted. Consequently, the potential for insufficient odorant in the vapor may be higher when the tank is full.
Explosive force Explosive force is dependant on the concentration of the gas in air. Most violent explosions occur at approximately twice the LEL where there is enough air for complete combustion. This concentration is called the Stochiometric concentration. Nat. gas- 10% Propane – 4%
Odorant detecting Factors Age,Health-colds, allergies Competing odors Some people cannot detect the odorant People sleeping nose shuts off when sleeping Odorant fade-new steel piping or steel tanks can absorb odorant! Soil can absorb odorant!
Gas Fire/Explosion Investigations Important considerations and guidelines to follow
Conditions leading to Fire/explosion What happened? Was anyone home and what where they doing? Should always try to interview victims some die later! Any gas or appliance work done lately? Any gas valves turned off or on? Was someone trying to light an appliance? Gas service disconnected or reconnected? Any appliances running or any problems? Anyone smell gas?
Conditions leading to Fire/explosion Last time tank filled? Anyone home? Was tank out of gas? Did gas company light pilots or check for leaks? What was weather like? Rain, snow, melting freezing temps, Flooding? If cylinders,location and when last filled?
Scene Examination Walk entire scene Follow entire gas system, source,piping, appliances,etc. Look at all gas valves and connections used and unused. Examine all appliances and note position of controls. Measure, sketch, photograph all equipment, piping before moving or testing. Photograph everything!!!!!!!!
Examine Gas System Start at gas meter or tank, then regulators etc. Note connections, valves, piping. Document all manufacturers, model, serial numbers. Look for breaks, holes, tears, etc. Check system for leaks before disturbing. Test should be at normal working pressure or less! Anymore can cause new leaks! Remember spoliation, might want to inform all potential parties before conducting any tests!
Special Propane Considerations Was this an out of service call? –If tank empty gas company is suppose to check entire system for leaks. –Including appliances, lines and valves. Gas company also to relight pilots for homeowner.
MYTHS ABOUT GAS EXPLOSIONS Propane explosions blow walls out at the bottom and natural gas blows out at the top! Propane exlosions are more destructive than natural gas explosions! Natural gas explosion presssures and flame fronts are as not as high or as fast as propane.