For
gas appliances, a flame supervision device (FSD) – alternative name: flame failure device (FFD) – is a general term for any device designed to stop
flammable
A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...
gas going to the burner of a gas appliance if the
flame
A flame (from Latin '' flamma'') is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction taking place in a thin zone. When flames are hot enough to have ionized gaseous components of sufficient density the ...
is extinguished. This is to prevent a dangerous buildup of gas within the appliance, its
chimney
A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler, stove, furnace, incinerator, or fireplace from human living areas. Chimneys are t ...
or the room.
Causes of flame failure include chimney downdraught, temporary interruption of the gas supply, gas under-pressure, liquid overspill on cooker hotplates or the
draught from an oven door being opened and closed.
FSDs may utilize one of several technologies:
thermoelectric valves,
flame conductance,
flame rectification,
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiati ...
sensing devices and liquid
expansion valves.
FSD usage in consumer products differs among political units – in the U.S., FSDs are not required by law or regulation for gas range (or gas stove) top burners and consequently are not present on ranges in the U.S. Cooker hotplates may not have a FSD on each burner. If a hotplate is to be used in a multi-occupancy building every burner must have its own FSD.
When the FSD activates it should stop (or reduce to safe levels) gas flow to the burner until it is reset manually.
Older devices, such as bimetallic strips, were used in conjunction with
pilot lights. The pilot light is no longer used in new devices, but may still be encountered on old appliances still in service.
Pilot lights were withdrawn because their continual small flame represented a waste of fuel.
Pilot lights required their own FSD, typically a thermocouple which held the valve open. Regular testing of FSD is a part of routine maintenance for gas appliances.
Other safety devices may be fitted in addition to an FSD. One type of these are the
Vitiation Sensing Devices,
that detect an adequate supply of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...
for efficient combustion, thus avoiding the production of poisonous
carbon monoxide
Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...
. As well as detecting a blocked supply of oxygen, these must also detect a blocked exhaust or reversed flow in the exhaust flue owing to wind conditions. Two methods are used to provide these, an Oxygen Depletion System (ODS) that measures the availability of oxygen for combustion or an Atmospheric Sensing Device (ASD) measures excess heat rise in the exhaust.
See also
*
Flame detector
References
{{Reflist
External links
Gas Flame Supervision Devices: Information at Falkirk Council, UK (Archived 14 December 2013; Accessed 2 January 2017)
Gas technologies
Heating, ventilation, and air conditioning
Natural gas safety