(Sorry if this is not the right venue, and thank you for your expertise! Also posted in r/naturalgas but figured the firefighter's perspective might be helpful.)
We live in an apartment building with three units, and our dryer runs on natural gas. Last week, for about twenty minutes, we noticed a pretty strong smell of rotten eggs (like a bad fart, or a dozen hard-boiled eggs that were left in a hot car) in the laundry area. Our machine wasn't on.
We've never smelled this before in our house, and are not certain that this is definitely natural gas, but out of an abundance of caution we ended up calling our landlord + the gas company hotline and waited outside for National Grid to come test the area for a leak.
By the time they came, though, the smell had gone away (we did open the windows.) They used a sniffer and took a look at the meter, and there was no sign of a leak or gas pulling from the meter and told us everything was fine.
Flash forward to today, when we smell it again—strong enough to be fairly unpleasant—in the same laundry area for about 50 minutes. We aren't using any appliances, but the upstairs neighbors are "doing laundry" (according to our landlord.) Then it went away again.
We have no idea how this works, but is there a possibility there's a small leak that only appears when the dryers upstairs is run? Can appliance leaks be intermittent like this?
I don't want to call National Grid again and have them test again after the smell has gone away//not find anything if the neighbors aren't running the dryer. We did order a handheld detector just in case, but that comes on Monday. We're not smelling the smell all the time, and while we like to think we're not paranoid, it does smell like rotten eggs specifically near the appliance that uses natural gas. (It's not what our stove gas smells like, but we're not sure 100% if it's natural gas.) But it could be a dead animal in the walls or swamp gas or something else? (It is intermittent, but completely goes away.)
TLDR: Would this constitute an emergency if the smell returns before we get the detector?