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 ppmVapor density -Natural gas 0.6 -Propane 1.5Ignition Temp Natural gas –900-1170 Propane-920-1120Heating 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.

Explosion Investigations

• Remember most leaks are caused by something someone did or didn’t do.

• How the gas leaked is more important than what ignited it.

• Any questions

• Thank you