Like I said before, I really don't know anything about these because it is a non-issue in my area. Here is something from the NFPA 54 (National Fuel Gas Code) handbook, however. (Bold added by me)
The following commentary was taken from the NFGC NFPA-54-2002 Handbook:
"The National Electrical Code requires a separate electrical circuit and over current protection for central heating equipment, as well as a means for disconnecting the power source at or within sight from the appliance. This separate circuit also can include circulating water pumps, valves, humidifiers, electronic air cleaners, and other accessories normally associated with the equipment. Certain appliances and installations also are permitted to be connected with a flexible cord that has a grounding-type attachment plug. The grounding-type attachment plug also serves as a disconnecting means for future service & maintenance. In subsection 8.6.4, note the phrase "a permanently live electrical circuit --that is, one that is not controlled by a light switch." This requirement thus prohibits "emergency shutoff" switches. In areas where oil is a common source of heating fuel, wall switches with red cover plates marked "Oil Burner Emergency Switch" are installed in buildings heated by fuel oil, as required by NFPA-31, Standard for the Installation of Oil-Burning Equipment, to stop the flow of oil to the burner. When converting an oil furnace or boiler to gas, the emergency switch must be removed. Emergency switches must not be installed when installing a new gas boiler. The emergency shutoff switch provides safety for oil-fired heating equipment, because failure of the boiler or furnace to shut off can prevent the oil pump from shutting off, thereby filling the equipment and surrounding area with oil. An oil pool fire is possibile. With gas-fuelded equipment, the emergency shutoff valve required in subsection 6.9.3 provides equivalent safety.
