Gas ExplosionsIreland Chapter IAAIBy Jamie NovakSaint Paul Fire and Safety servicesNovak Investigations

Properties of natural and Propane gasNatural gas LEL lower explosion limit 5%-45,000ppNatural gas UEL upper explosion limit 15%100,000ppmPropane gas LEL 2.15% 22,500 ppmPropane gas UEL 9.60% 95,000 ppmVapor density -Natural gas 0.6 -Propane 1.5Ignition Temp Natural gas 900-1170 Propane-920-1120Heating Value BTU/FT3-Nat-1000 Propane-2488

OdorantMercaptans are generally used to odorize fuel gasesNatural 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

OdorantSince 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 forceExplosive 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 FactorsAge,Health-colds, allergiesCompeting odors Some people cannot detect the odorantPeople sleeping nose shuts off when sleepingOdorant fade-new steel piping or steel tanks can absorb odorant!Soil can absorb odorant!

EXPLOSIVE LIMITSPropane (RED)Lower Explosive Limit 187 Bits (22,500 PPMUpper Explosive Limit 212 Bits (95,000 PPM)Natural Gas (BLUE)Lower Explosive Limit 208 Bits (45,000 PPMUpper Explosive Limit 225 Bits (100,000 PPM

Gas Fire/Explosion InvestigationsImportant considerations and guidelines to follow

Conditions leading to Fire/explosionWhat 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/explosionLast 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 ExaminationWalk entire sceneFollow 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 SystemStart 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 ConsiderationsWas 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 EXPLOSIONSPropane 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.

Explosion Investigations

Remember most leaks are caused by something someone did or didnt do.How the gas leaked is more important than what ignited it.

Any questions

Thank you