Sometimes they are also installed in locations where the plumbing code does not require a primer because of a high probability of the trap drying out, but because of a nearby ignition source and the explosion hazard in the event that the trap did leak sewer gas. Most designs require installation in an accessible location where periodic maintenance can be performed.
Sometimes they are installed in areas where plumbing codes do not mandate a primer due to a high likelihood of trap drying out, but because of an adjacent ignition source and the risk of explosion if the trap leaks sewer gas. Most designs necessitate installation in a location that allows for periodic maintenance.