The smell of sewer gas coming out of a drain is a sign something's wrong, though the remedy is often as simple as pouring water down the drain. Most people think of an evaporating water seal in a p-trap when they smell bad odors, so it can be frustrating to add water only to still have the odor around. There are other causes, though, and while they aren't cause for alarm, they definitely need fast action because once you've smelled that rotting odor, you never want to smell it again.
Broken Bypass Plug
If you're sure the smell is from sewer gas, and you've just poured a lot of water down the drain, the problem might be at the bypass plug. Floor drains often have a bypass valve that lets you send things like a drain snake down to break up clogs. This valve has a plug that normally seals the opening so sewer gas can't get out. If the plug breaks (or even loosens up), all that sewer gas is going to pour into the room. You'll need a plumber to fix the plug or install a new drain.
As you can imagine, opening that plugged valve to use a drain snake would let that sewer gas into the room anyway, even if the plug normally worked well. If you smell gas, and you've just had repairs done, there's your culprit. And keep in mind, you don't have to have just had repairs done that day. If the room is not normally vented well, that gas can hang around.
There's not much you can do here except really open up the room. Open windows, prop open doors, set fans so they're blowing air out of the room, and so on. The smell should disappear once the room has been thoroughly aired out.
Food Where It Shouldn't Be
One more potential cause could be occurring when you smell something that you think might be sewer gas, but you're not sure. If your floor drain has a filter that isn't locked down, you could be dealing with old food that's started to rot. Unfortunately, sometimes you get an employee who doesn't bother to sweep up things like food scraps in commercial kitchens, instead pushing them into the drains for disposal. The food can catch on the filter and rot. Have the drain cleaned and then get a locking filter.
You can always call a drain specialist to install a new, clean drain if you've been having too many problems with the old one. Get a locking filter, a new bypass plug, and new traps if needed, and you should see those odors disappear quickly. Contact companies like Sani-Floors for more help.