Ummm. As a repairman for a gas utility company, my experience was that about 99% of all gas leaks are so small that they are not an actual hazard of causing a fire or explosion.
However, pretty much all utility companies dispatch people at once to check out any gas leak, and are intolerent of allowing any detectable gas leak from remaining in a system.
The reasons for that are 1) unless you have inspected the entire system, you can never know if a gas odor is is among the 99% that aren't an actual hazard or the 1% that are. 2) Unless you are trained and experienced, people can't classify leaks accurately 3) A gas odor is a warning of a possible hazard. If people get used to tolerating a small leak, that warning is effectively obliterated and a more serious problem may be ignored 4) the lawyers will crucify you if you are wrong.
BY FAR the most numerous genuinely hazardous natural gas leaks are from gas mains and services that can saturate the ground with gas that then infiltrates basements and crawl spaces, allowing large volumes of gas to accumulate which then can literally blow a building off it's foundation.
Because those leaks are the largest real danger, I was trained to check basements, crawl spaces and the perimeter foundation for gas before checking anything else, unless a leak is something like a broken pipe in a house where the cause is more obvious and immediete.
That is very good advice for service personnel as well ---- DON'T start hunting around for a little fizzzer unless you have already checked for leakage in basements, crawl spaces and around building foundations.
The practice of my utility was that if we found MEASURABLE amounts of gas in the air inside a building, or expolsive levels of gas against an outside building wall, we left the building immedietely, evacuating anyone we could while on our way out. The fire Department was then notified to help evacuate neighboring buildings before any attempt was made to stop the leakage.
To measure gas in air, we had calibrated meters that measured the percentage of gas in the air and the percentage of the lower explosive limit of the gas in air ---- so 2% gas in air was 50% LEL (lower explosive limit) since natural gas is explosive in the 4-14% range.
Despite the fact that little fizzers are only very infrequently an actual hazard, we routinely shut off and red tagged equipment if we could not correct the problem, for the reasons described earlier.
Technicians working on gas equipment might want to ask their gas utility to send out a technician or trainer to discuss how to deal with natural gas hazards, especially hazards created by leaking gas mains and services.
I might add that leaks from gas mains and services are quite common. When detected, utility repairman like myself classified the leaks to determine whether they were an actual hazard ---- if they were, they would be repaired immedietely.
But 99% were not an immediete hazard. These would be checked again on a daily, weekly, monthly or annual basis to determine the extent of the hazard, and might not be repaired for years.
During my years with the utility, I evacuated several dozen buildings because of gas leakage hazards. A very few were extremely dangerous and scared the XXXX out of me. Almost all of those were gas in crawl spaces or basements or gas against the building foundation. Keep in mind that if gas is just against the foundation of a building but not inside the building, the building next door may have the basement loaded with gas and be ready to blow up any second, which will likely blow you up too.
The bottom line is ----don't spend time looking for a little fizzer until you've eliminated gas in basements, crawl spaces and foundations, which is what is likely to kill you, and other people in the neighborhood. A good gas leak that has been saturating a neighborhood may cause several buildings to blow up in a chain reaction, with one touching off an explosion in another. So get a long distance away from a building if you find significant gas in the room or crawl space air or building foundation.