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Why doesn't gas have same safety rules as electricity?

Question asked by dmahalko on Sep 21, 2018
Latest reply on Sep 24, 2018 by milt.werner

I am not a professional in any regard, just a tech hobbyist that contributes on Wikipedia / Stack Exchange / Quora, etc.

 

Regarding the recent gas explosions in Massachusetts, I am left to wonder how it is that gas technology has been in use for as long as it has, with it managing to escape the same life-safety protection systems that are commonly in use everywhere for electrical circuits. It is very bizarre.

 

Circuit / appliance isolation:

  • Electrical circuits in buildings are required to be isolated into separate circuits leading back to a circuit panel.
  • Gas just strings one big long continuous pipe from one device to the next and does not use a circuit panel with separate on/off switches for each device.

 

Overcurrent protection:

  • Electrical circuits in buildings have amperage-based overcurrent protection at the circuit panel so that if a device malfunctions and draws too much power, it is cut off and isolated so that damage is limited.
  • Gas has effectively no overcurrent / high-flow detection whatsoever. If a $10 flexible pipe joining a clothes dryer to the gas line breaks off, there is nothing to prevent the gas from spewing out as fast as possible until the building fills with gas and a spark triggers an explosion.
  • With regard to the Massachusetts gas main overpressure, this will of course cause gas to spew out of running appliances at a much higher rate than normal, potentially resulting in dangerously huge flames, overheating, and spread of fire around the appliances. An overcurrent gas breaker on an isolated circuit for each gas appliance would have been able to cut off this abnormally high flow through the appliances before it became dangerous.
  • Not only is there not per-device overcurrent protection, there is no building-wide overcurrent protection. There is no such thing as a MAIN gas breaker. 

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If we installed electric circuits the same way we installed gas, we would just have a huge 200 amp on/off switch connecting the building to the pole transformer, run it through a meter, then directly run that 200 amp cable from the meter into the building to the kitchen stove, and then continue that 200 amp cable to the water heater, and then continue the 200 amp cable to the electric central heating furnace in the basement. all without fuses or circuit breakers of any kind.

 

If this huge 200 amp cable were to break, and you see huge blue arcing or hear a loud ominous buzzing, there is just nothing to be done about it except flee the building, call the electric utility to come shut it off, and hope your house doesn't burn down before they arrive.

 

This sounds clearly nuts, but this is how gas is installed and used in residential homes everywhere.

 

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And it's not like a gas "over current breaker" is too complicated to make either. It's just a spinning metering device with a mechanical speedometer on it. If the flow rate exceeds a certain speed, close the circuit with a ball valve and spring. If slow-blow is needed to prevent startup false-tripping, this can be provided with mechanical dash pots.

 

If a gas main breaks in the street from a backhoe, with a huge flame 50 feet in the air, there are no automatic protections to stop this. Someone from the gas utility has to be called in to shut it off. Why can't there be over-current circuit breakers for the street gas mains?

 

It's just weird how electricity has all these life safety protections established by the NFPA, while gas has none of it at all.

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