Book 29 Gas Utilities Flashcards
Book 29 Gas Utilities
Pure natural gas is completely odorless.
odorant is added so that as little as ___-percent of natural gas in the air can be detected.
The common odorant is a ______ mix, which is used in solution of one pint per million cubic feet of gas.
one
Mercapitan/Thiophane
Book 29 Gas Utilities
Natural gas is non-toxic and is not considered hazardous when inhaled in limited concentrations.
However, in quantities large enough to displace oxygen,
asphixiation can occur.
reference
Book 29 Gas Utilities
Natural gas is _____ than air
lighter
escaping natural gas rising and rapidly dissipating.
This is a distinct safety advantage over heavier fuels such as butane and propane, which are heavier than air; and when escaping, it will collect in low areas.
Book 29 Gas Utilities
Natural gas also has an ignition temperature of ___ degrees
Flammable range between ___ and ___ percent.
1100
4 and 14
Book 29 Gas Utilities
Transmission lines maintain pressures up to ____ psi and use pressure booster compressor stations, at specific intervals, to maintain appropriate flow and pressures.
1000
Book 29 Gas Utilities
Transmission lines bring natural gas into the Southern California area and vary in diameter from ___ to ___ inches.
12 to 36”
Book 29 Gas Utilities
Natural gas is then distributed to Gas Company customers by distribution mains.
The gas is carried by service lines, as medium pressure, which normally does not exceed ___ psi.
60
Book 29 Gas Utilities
At the service meter (Meter Set Assembly), the pressure is reduced to a low pressure (approximately ___ psi.).
1/3
Book 29 Gas Utilities
Distribution mains are generally polyethylene and account for a high percentage of the mains in use today.
Older existing distribution mains are made of steel or copper, but are rare to find.
Polyethylene mains are color coded to identify the pipe as
transporting natural gas. These pipes are yellow, which is the national color code for newer installations. Older installations of plastic pipe can be pink (salmon beige), or orange in color.
Polyethylene will have a wire running the length of the pipe, for locating plastic gas lines, below ground.
Above ground gas lines must be made of steel and cannot be plastic.
Distribution mains are normally located underneath city streets, parallel to curbs, under grassy parkways, between the curb and sidewalk, and occasionally in alleys.
reference
Book 29 Gas Utilities
A ring on the stopcock valve indicates a ______.
A band on the stopcock valve indicates the service line is plastic.
branch service
Book 29 Gas Utilities
A flat washer on the stopcock valve indicates that the?
service line is a plastic pipe inserted inside an older metal pipe.
Book 29 Gas Utilities
Next, up the riser, is a flat circular device called a “regulator” that reduces medium gas pressure (up to 60
psi) to a relatively low level of approximately 1/3 psi.
Next are pipes and fittings, leading to the gas meter. The meter measures the amount of gas that is used.
After the meter, gas flows through pipes and fittings into the structure.
reference
Book 29 Gas Utilities
A “G”, required by Cal-OSHA, marks the location where the
service line passes beneath the curb and indicates which side of the building the MSA is ocated.
reference
Book 29 Gas Utilities
Some MSA’s may be equipped with an emergency vibration-sensitive shut off device known as an earthquake
valve. These valves are marketed by private industry and are normally mounted on the discharge side, right side as you face the meter, of an MSA.
Personnel should recognize and understand that a swift-kick may possibly shut off the flow of gas, but only in the event of a damaged or frozen stopcock;
reference
Book 29 Gas Utilities
Industrial shut-off valves, known as Nordstrom valves, are used for high pressure applications.
Some industrial installations have gate valves with wheel handles that may be turned clockwise to close.
reference
Book 29 Gas Utilities
Meters under the sidewalk, called curb meters, are common in commercial areas. The lid over the curb meter space is made of lightweight concrete, or fiberglass set in a metal frame, and is easily identified by its gas company markings.
reference
Book 29 Gas Utilities
BRANCH SERVICE
In some commercial areas, multiple structures may be commonly serviced by a single service pipe called a standard service main.
A metal ring identifies this branch service.
The occupancy that is further from the supply main is a standard service, and the other occupancies are branch services.
All MSA’s that are served from the branch main will be identified by a ring at the stopcock.
reference
Book 29 Gas Utilities
Stuck tangs can be approached in EMERGENCY CONDITIONS as follows:
- Use two wrenches, one on the tang and the other on the backing nut. Holding the tang steady, loosen the backing nut one-quarter turn only! If the backing nut is loosened too far, the core can fly out, leaking medium pressure gas, 40 to 60 psi.
- Give the backing nut a tap with a non-metallic hammer, freeing the core.
- Turn the tang, one-quarter turn, to stop the flow of gas; a half-turn will continue to let the gas flow.
- Tighten the backing nut to lock the core in the “OFF” position.
reference
Book 29 Gas Utilities
The Nordstrum Valve is a larger version of a residential stopcock. It is used on high-pressure risers and piping, at industrial/ commercial sites, and comes in various sizes to fit different diameter pipes.
reference
Book 29 Gas Utilities
CURB VALVES
Also referred to as an Emergency Shutoff Valve. These valves can be installed in addition to stopcocks at public assembly occupancies such as schools, hospitals, churches, etc.
reference
Book 29 Gas Utilities
The greatest danger results from gas leaks inside structures, due to the potential for ignition and explosion.
reference
Book 29 Gas Utilities
For faint odors, always check the condition of pilot lights as a first action.
reference
Book 29 Gas Utilities
Tactical considerations at an inside leak should include the following considerations:
Determining necessity and extent of evacuation.
Remove all sources of ignition. Avoid operating electrical switches. Turning a switch “ON” or “OFF”, can cause sparking. Also, avoid walking on carpets in dry weather to prevent sparks from static electricity.
Turn off appliance valve located at the connection from the appliance to the customer house line.
Open windows after all sources of ignition have been eliminated. This ventilation can bring the gas into the proper explosive mixture with air.
Searching for occupants who may be overcome by gas.
If it is determined to be unsafe to enter the structure, consider the following:
Turn off gas at the meter.
Spot apparatus in safe zones.
Establish a water supply and prepare for fire suppression operations.
reference
Book 29 Gas Utilities
Leaks outside structures
The Fire Department’s role at the site is to maintain public safety. This usually means eliminating potential sources of ignition until the leak is stopped.
reference
