Why does our gas kiln smell approaching it's leak gas when looking after say it's not? Our apartment came near an old huge undo flame gas heater. When...

Our apartment came near an old huge undo flame gas heater. When we run it there's a STRONG gas smell, so desperate you can barely breath. Maintenance have checked it for leaks and found none. Our other, smaller and newer, gas furnace does not do this.
Answers:    The old space heater may not be burning as efficiently as the newer electric fire hence the smell of mercaptan*.

Sometimes there's a burner air adjustment.
Some gas suppliers will inspect/adjust as required.
Call your local fire department, relate the situation, and ask them other to send someone to check it.