Fluid Flow Sensors

• http://www.mcmillancompany.com/products/101.htm I don't know if it will blow up with something flammable, but by the looks of it, it is designed to be safe. I would ask them, anyway. It doesn't provide pulses for it's output, but rater a 0-5v signal, corresponding to a 0-100% flow. They provide a few other flow sensors -- high pressure, Teflon coated innards some that provide pulsed output, etc.
• http://www.designinfo.com/scripts/makeframe.dll?Url=http%3A//www.designinfo.com/help/Flow.html Just put in all your specs, click search, and it lists all that look like they might be what you want.