I previously missed the comment about electric motors in the garage. Unless your appliances are truly ancient the motors are sealed units and are induction motors anyway with no brushes and comutator to spark. The thermostat on a frige or freezer can spark but I don't know if they are selaed away or exposed to potentially explosive vapors on your models.
Not that I recommend getting one but for general interest there are instruments with sensors that take a reading on the atmosphere and test it for combustibility...sort of a fuel-air ratio thingy. Some have setable alarms for the level you want to have it trip off, start a ventilation fan, or whatever.
[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]