Chapter 12 Gas Utilities Flashcards
What odorant is commonly added to natural gas?
Thiophane
Newer distribution mains of polyethylene are recognizable by what color?
Pink or bright orange
What are the primary components of a meter set assembly?
Piping, shutoff valve, regulator, and meter
What does a green band on a riser near a stopcock valve indicate?
The service line is plastic
Why are rotary meters used?
To regulate high pressures and to handle quick surges
To turn off the flow of gas with a stopcock valve, you should turn the tang to what position?
Crosswise to the pipe
To eliminate the flow of gas to a multiunit dwelling, which stopcock should you shut off?
The stopcock on the common riser
Who should restore the flow of gas to a building when the supply has been shut off?
Only a gas company representative
What are the three categories of natural gas emergencies?
Inside leaks, outside leaks, and leaks resulting from fires
Normally, what type of gas leak poses the greatest danger?
Gas leaks inside structures that present the potential for an explosion
Natural gas supplies approx. ___ of the energy requirements of the U.S.
1/3
What hydrocarbons is natural gas generally comprised of?
Methane and Ethane
What chemical impurities can be present in natural gas?
Nitrogen, carbon dioxide, hydrogen sulfide, helium
What percent of natural gas is methane?
97 PERCENT
What may be used in natural gas at 400 parts per million and used for identification? how?
Helium
Seepage from underground storage or breaks in gas lines can be differentiated from seepage from natural underground pockets
What concentrations is Thiophane used in natural gas?
1 pint per million cubic feet
Natural gas transmission lines have pressures up to what PSI?
1000 PSI
How big are transmission lines?
12-36 inches
What pressure can be found in distribution mains?
60 psi
What are distribution mains made out of?
Older–steel or copper
Newer–polyethylene
What color are polyethylene distribution mains?
Pink or bright orange
What is the pressure inside customer gas lines?
1/3 psi
How is the pressure in a customer line regulated?
regulator and gas meter
What is a MSA and what 3 locations can these be found?
Meter Set Assembly
Outside sets–outside of structure
underneath sets–underneath structures, stairs..
Curb meter box–vault underneath sidewalk
What does a MSA consist of?
Piping
shut-off valve
regulator
gas meter
What is a riser?
pipe rising vertically from the ground close to the exterior wall of a structure
What is a shut-off valve called?
stopcock or service cock
What does a flat washer on the stopcock indicate?
service line is plastic pipe inserted inside an older metal pipe
What does a ring on the stopcock valve indicate?
branch service
What does a band (normally green) on the riser near the stopcock indicate?
service line is plastic
What pressure does the regulator receive? what does it reduce it down to?
60 psi–down to 1/3 psi
What is an earthquake valve?
emergency vibration-sensitive shutoff device
What is a Nordstrum valve? How far can the tang be turned?
an industrial shutoff valve used for high-pressure applications
The tang can only be turned 1/8th turn
When dealing with branch service, what occupancy has the standard service? the others are branch service
the occupancy farthest from the supply main
Generally, what is the safest and most direct method of eliminating the flow of gas to a structure?
turn it off at the stopcock
What does a basic stopcock consist of?
Internal core Casing Washer backing nut circlip
What does a G chiseled or painted on the curb indicate?
required by OSHA–shows the location where the service line passes beneath the curb and indicates the side of the building on which the MSA is located
In an emergency situation where the stopcock wont turn, how might you free it up to turn?
Loosen the backing nut up ONE TURN ONLY. tap the backing nut with non-metallic hammer,and turn 1/4 turn
What are the 3 primary objectives when dealing with a gas leak emergency?
Safety
Protection of Property
Prompt and efficient control of incident
What 3 categories can natural gas be divided into?
Inside leaks
Outside leaks
Leaks resulting in fires
What is a service entrance cock?
It is a master valve where the service enters the building
What is the best immediate procedure for responding to an outside leak?
Call the gas company
Of all the decisions to be made, what has the most variables?
Where to stop a leak
Pipe lines may contain hazardous contaminates known as what?
PCBs–Polychlorinated biphenyls
