Stromness 13 Feb 2016 – The question of the smokey fire

Safety First – fire = heat, fuel (carbon) and oxygen (o2).  When these 3 are correctly balanced the fuel turns to carbon dioxide (co2) and water (H2O) when burnt.  When they have inadequate oxygen the fuel turns to Carbon Monoxide an odourless, deadly gas which will put you to sleep before killing you. 

Therefore all open fires must be correctly installed by a Registered Engineer and must meet the requirements of Building Regulations.  The engineer will ensure that there is sufficient oxygen available via vents.

 A Smokey fire is a warning that something is wrong, it must be put out immediately and not used until corrected by a Registered Engineer.

 TheScience of a Smokey Fire:

 A Volume of gas increases as pressure reduces and reduces as pressure increases therefore it will expand to fill the available space or can be directed by physical forces where ever you want it to go

 When a fuel (say coal) is burnt it alters its state from a solid to a gas. The emitted gasses and particles (fumes) will fill a room if no other physical forces are in place.  The physical forces which generally act on these gasses are as follows:

Heat which will force the gasses upwards

A flue within a chimney which will force warm gasses upwards

Therefore if the fire is placed directly beneath the flue within the chimney the fumes will move upwards within the flue unless stopped by other forces such as:

 If the flue is cold a plug of cold air can restrict or prevent the fumes

Down draft from winds above can blow the fumes backwards

The fire opening must be less than 8 times the flue cross sectional area or the up draft will be inadequate and fumes will spill into the room

If the combustion is inadequate insufficient heat will be generated to assist the updraft and smoke and deadly carbon mon-oxide will enter the room