Flame Failure Devices
A flame failure device monitors the flame on a gas stove's burner, and stops the flow of gas to the burner if the flame goes out. These devices use a thermocouple that generates a small electric current when it is heated by the burner's flame, and the electric current activates a valve on the gas supply line, keeping it open as long as the flame is present. If the flame goes out, the thermocouple doesn't generate current, and the valve closes. The action of the device prevents gas from building up without being combusted.
Some flame failure devices require the stove's user to manually restart the flow of gas after the flame goes out, but the devices used in many gas cooktops trigger an automatic re-ignition system that relights the burner flame after it goes out. In this case, an electronic circuit monitors the flame and the burner switch; if the switch is on and there is no flame, the circuit triggers an electronic igniter, which uses an electrically produced spark to ignite the gas.
Combustion in gas stoves produces harmful gases such as carbon monoxide and nitrogen dioxide; the latter can cause respiratory irritation, and the former can be fatal if it builds up inside your home. In addition, cooking on the stove produces fine particulate matter that can cause respiratory complications, and airborne grease from cooking can build up on surfaces and create a fire hazard. Most gas cooktops are equipped with vent hoods that vent these harmful substances to the outside; a fan in the hood draws gases and particulate matter into a duct that exhausts the substances to the exterior of the building.
Where venting exhaust from the stove is not possible or practical, some gas stoves employ filtration systems that remove some particulate matter from the air. Activated charcoal and wire mesh in the filters work to remove grease and cooking odors from the air above the stove. These filters do not remove harmful gases, however, or even all of the grease and particulate matter, so a properly vented range hood is preferable as a safety device.