BOOK 29 CH. 6 Flashcards
Natural gas also has an ignition temperature of 1100 degrees, and has a flammable range between 4 and 14 percent.
Natural gas is non-toxic and is not considered hazardous when inhaled in limited concentrations.
Transmission lines bring natural gas into the Southern California area and vary in diameter from 12 to 36 inches.
The gas is carried by service lines, as medium pressure, which normally does not exceed 60 psi
At the service meter (Meter Set Assembly), the pressure is reduced to a low pressure (approximately 1/3 psi.)
Additionally, MSA’s can be categorized as follows:
Residential
Industrial
Multiple Gas Meter
The pipe rising vertically from the ground, close to the exterior wall of a structure is called a riser. Tracing the riser up from the ground, the first fitting is the shut- off valve called a stopcock or service cock.
personnel responsible for shutting off the gas to a structure. Of particular interest is the following:
A ring on the stopcock valve indicates a branch service.
A flat washer on the stopcock valve indicates that the service line is a plastic pipe inserted inside an older metal pipe.
A band on the stopcock valve indicates the service line is plastic.
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.
Shutoff valves can be located by finding the MSA since they are always adjacent to each other. Initially, look for a “G” that is either chiseled or painted on the curb.
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. If a “G” cannot be quickly found, do not waste time looking for one.
If an MSA is not visible along an outside wall, it is usually found in the following location:
In a crawl space, under the building.
Beneath an outside staircase.
In an outdoor cabinet, particularly new condos.
In an underground garage.
In a sidewalk or parkway vault, at the side of a building.
In a basement, with the shut-off valve usually accessible from the outside of the building.
Subsurface, in the parkway or sidewalk.
MULTIPLE METER SET ASSEMBLIES
Multiple habitational or commercial occupancies are often equipped with multiple MSA’s, which provide a master stopcock and a separate meter and stopcock for each unit. Past the riser, and master stopcock, is a horizontal header that feeds multiple stopcocks and MSAs.
A metal ring identifies this branch service.
The tang on some stopcocks can be square. Turn the tang, so the line on the tang is crosswise to the pipe. Tangs can be easily turned with a crescent wrench.
- 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. It is nearly impossible to replace the core while gas is leaking.
