How To Stop A Gas Leak

Transcription

1 Natural Gas / Propane Emergencies Probationary Firefighter Academy

2 Properties of Natural Gas / Propane Natural Gas and Propane are gaseous fossil fuels Natural Gas is primarily Methane(CH 4 ) Propane is (C 3 H 8 )

3 Properties of Natural Gas / Propane Methane and Propane are defined as a simple asphyxiants It displaces oxygen They are both non-toxic They do not chemically bond with your blood like Carbon Monoxide

4 Properties of Natural Gas / Propane Methane is lighter than air and will dissipate quickly in an open area Propane is heavier than air and will collect in low lying areas

5 Properties of Natural Gas / Propane Click Image to Play Video Both gases are colorless and odorless gas Odorant is added to these gases to assist with detecting leaks. Methyl Mercaptan is used as an odorant and is a hydrocarbon compound containing sulfur Methyl Mercaptan is heavier than air (VD = 1.66) and tends to fall out of natural gas when it is released from its container or pipeline

6 Properties of Natural Gas / Propane There are times when natural gas is not odorized: when it is transported via interstate pipeline when it is in a liquefied state when it is stored as a cryogenic fluid Propane may also be unodorized when transported via pipeline

7 Properties of Natural Gas / Propane The only way to truly confirm the presence of natural gas or propane is by direct reading flammable gas detectors

8 States of Natural Gas Liquified (LNG) Condensed into a liquid at close to atmospheric pressure (3.6 psi max) by cooling it to approximately F. LNG is not odorized The expansion ratio is 600:1 from its liquid volume to its vapor state Compressed (CNG) Compressed under high pressure (up to 4000 psi) not liquefied CNG is odorized

9 Vehicle Fuel May be used to fuel vehicles as an alternative to gasoline or diesel Vehicles fueled by CNG can be identified by a diamondshaped decal displaying the initials CNG or LNG Vehicles with LNG will have gas detection systems (because the LNG will be odorless)

10 Pipelines Natural Gas is transported in pipelines ranging in size from 36 interstate pipelines to ½ service drops Pressures can range from ounces to pressures above 500 psi

11 Natural Gas Pipelines Texas has more intrastate natural gas pipeline miles (over 43,000) than any other state

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13 Operating at the Gas Incident Approach the emergency from upwind, if possible Evacuate the immediate area Secure a Hot Zone of sufficient size and configuration to ensure that ignition will not occur Eliminate all potential sources of ignition in the Hot Zone Require that any person, including gas utility company personnel, entering the Hot Zone be equipped with the proper protective gear In those cases where ignition has occurred or is likely to occur, provide hose lines of sufficient capacity to protect any exposures that are within the Hot Zone Provide fire protection and rescue standby for those entering the Hot Zone

14 Establishing the Hot and Warm Zones There are 2 ways to establish the Hot Zone and Warm Zone Atmospheric Measuring: using meters to get direct readings of % of LEL present Rules of Thumb based on the type of container involved

15 Atmospheric Measuring (Meters) The Hot Zone boundary is established by atmospheric monitoring and should encompass an area where readings are at or above 10% LEL The boundary of the warm zone is where readings do not exceed 1% of the LEL 10%+ LEL 1%-9% LEL

16 EXAMPLE Hot Zone Rules of Thumb Pipeline Release 2 in. line x 8. Diameter of gas pipe (in inches) x = Hot Zone radius in feet ft. radius For pipes 8 inches or larger evacuate a minimum radius of 150 ft. Monitoring should be used to confirm levels outside the hot zone are below 10% LEL. The distance established by this formula helps create an adequate isolation area for a typical release and in case of ignition

17 Hot Zone Rules of Thumb CNG Leak: An initial Hot Zone with a radius of 50 ft should be established CNG Fire: Evacuation distance is expanded based on size of container LNG Leak: An initial Hot Zone with a radius of 75 ft should be established The 2004 ERG recommends an evacuation distance of 1 mile for rail car and tank truck fires Containers involved in fire Small tank (20 lbs) Large tank (100 lbs) Residential or commercial tank (2,000 lbs) Small bobtail truck (8,000 lbs) Big truck (40,000 lbs) evacuate 160 ft. evacuate 275 ft. evacuate 750 ft evacuate 1175 ft. evacuate 2000 ft.

18 Gas Release Inside Structures Since structures do not allow the gas to dissipate, extra care must be given Evacuate the building Eliminate ignition sources Main breaker Shut off main gas shut off (eliminate pilot lights) Enter area with PPE and atmospheric monitoring Natural Gas will collect higher areas Propane will collect in low areas Ventilate to remove gas from building

19 Gas Line Valves The key to mitigating a gas emergency is to shut off the fuel supply. Often the simplest and safest way to do that is to shut of the supply valve.

20 Gas Line Valves Multiple meters off a single feed Meter shut-off Meter shut-off Main supply valve

21 Gas Line Valves Click Image to Play Video

22 Ignition of Gas Leaks Evacuate and secure an area of sufficient size to prevent injury to the public Provide hose lines with sufficient volume to protect exposures within the area affected by radiant heat from the fire DO NOT ATTEMPT TO EXTINGUISH THE FIRE! Extinguishing the fire will allow gas to escape and spread. The fire should be extinguished by shutting off the fuel supply

23 Container Fires CNG The cylinder has a fusible plug melts that melts at 212F and it is not possible to shut off the flow from a cylinder after this has happened If the cylinder is not compromised, the fire may be controlled by accessing a control valve or emergency shut off LNG Do not spray water on leaking containers or any spilled liquid. This will heat the container or the spilled LNG and increase the vapor expansion rate Do use a hose stream to protect the container if it is threatened by fire

24 Mitigation of Pipeline Incidents Flow from a pipe can be stopped by: Closing a valve Plugging the line Squeezing off the line The tactics used will depend on the type of pipe material and the size of the line.

25 Mitigation of Pipeline Incidents Cast Iron Pipe and PVC Pipe: Cast Iron is old and too fragile for squeeze-off or plugging PVC is also too brittle for squeeze-off and plugging operations Establish hot zone and protect exposures Eliminate ignition sources Gas company will have to stop the flow of the line

26 Mitigation of Pipeline Incidents Steel Pipe If the break is clean enough, the line can be plugged Responders must be in full PPE and on air A backup team must be in place with a charged hoseline (minimum 1 ¾ )

27 Mitigation of Pipeline Incidents RES501 carries a pipe plugging kit. It is typically used for metal natural gas lines. It is not to be used on plastic pipes. Plastic lines are too slick for the plugs to stay reliably secure.

28 Mitigation of Pipeline Incidents The proper size plug is placed on the T handle and placed into the open pipe. The T handle is tightened to cause the rubber plug to be compressed. It bulges out and presses against the inside walls of the pipe to secure the plug in place

29 Mitigation of Pipeline Incidents The T handle is then released from the plug and a second plug is applied on top of the first as a safety measure. Responders should not place themselves in front of the pipe opening as excessive pressure can shoot the plug out of the pipe. Mitigation personnel must also wear hearing protection (ear plugs) as the pitch of the escaping gas will increase as the opening is restricted

30 Mitigation of Pipeline Incidents Polyethylene Pipe Used extensively over the last several years. Very common as feeds from the street to a residential meter Common sizes: ¾, 1, 1 ½, 2 These lines are pliable enough to be squeezed shut If without squeezers, smaller lines can be folded over and taped to stop or slow flow The internal walls are too smooth for plugs to work effectively

31 Mitigation of Pipeline Incidents Polyethylene Pipe Very susceptible to static electricity build up Use a grounding tool or wet the ground around the pipe to help dissipate static charge

32 Mitigation of Pipeline Incidents MVFD has two types of gas line squeeze-off tools to stop the flow of natural gas from polypropylene supply lines

33 Mitigation of Pipeline Incidents The older squeeze-off clamps are red and operate on ¾ and 1 gas lines. Anytime crews operate at a gas leak, a charged hoseline should be manned to protect the team operating the tool.

34 Mitigation of Pipeline Incidents The newer squeeze-off clamp is designed to work on lines as large as 2-inch. This tool is also equipped with a grounding rod to prevent static electricity discharge between the tool and the leaking pipe. The grounding rod should be in the ground before the tool is applied to the pipe.

35 Mitigation of Pipeline Incidents The lower jaw of the clamp should be rotated so that the proper pipe size lines up with the indicator on the tool.

36 Mitigation of Pipeline Incidents The clamp also has handle extensions to increase leverage on the tool.

37 Mitigation of Pipeline Incidents Once the gas line is squeezed off, the user should ensure that the pin is in Locked position. (The tool can be closed on the line with the pin already in the Locked position)

38 Propane Tanks Tanks used for residential and commercial buildings typically range from 250 to 1000 gallon capacities.

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40 Propane Tanks Smaller tanks, such as the 20 pound tank are used for BBQ grills, travel trailers, mushroom heaters, and a variety of other devices. Overfill protection device

41 Propane Tanks One of the greatest dangers of a propane tank exposed to fire is the possibility of a BLEVE Boiling Liquid Expanding Vapor Explosion Occurs when fire impinges on the out shell of the tank in the vapor space of the tank. With no liquid in contact with that portion of the tank, there is nothing to dissipate the heat from the shell. The metal weakens and then expands due to the internal pressure of the tank. The tank then fails at this point.

42 Propane Tanks BLEVE Protection is accomplished by cooling the vapor space of the tank shell with hose streams. The area should be sound from the evacuated if the relief valve increases in pitch while streams are being applied.

43 Propane Tanks Click Image to Play Video BLEVE Demonstration:

44 Case Study On January 30, 2007, a propane leak occurred during the offload of a tank at the Little General Store in Ghent, West Virginia. The video link below shows the events leading up to the explosion and loss of life that day as well as recommendations to prevent future tragedies. Click to Play Video