FEATURE |
INCORPORATING COLD CHAIN |
||||
|
on electronic systems that detect fires early and rather reduce the risk of fires starting or spreading in the first place .”
Installation errors are rare . “ The system is installed in line with the ducting by the mechanical contractor that installs the air conditioning system . A mistake that could be made is to install it the wrong way around . The fusible link has to be installed facing the direction from which the air is entering . This is unlikely if a reputable contractor is used ,” says Bosch .
THE FIRE ENGINEER
Karel Roodt , director and engineer at The Fire Engineer , lists the three basic essentials of fire protection :
• Study of fire : To learn the causes of fire , fire extinguishing techniques , detection and extinguishing equipment and their uses , and the rules and regulations related to building construction
• Active fire protection : Includes manual or automatic detection of fire , the use of fire and smoke alarms , fire suppression , firefighting , and first aid firefighting
• Passive fire protection : Design of building and infrastructures , use of fire resistant material in construction , provision of isolating fire , fire walls and doors , smoke doors , signage , markings , and evacuation plans
“ Even with the most comprehensive fire safety provisions that modern technology can provide , it is essential that there be adequate management of fire safety to ensure that the occupants of a building or facility reach a place of safety in the event of fire and to avert disaster . In many multi-fatality disasters and business losses , poor fire safety management has been found to be a significant contributing factor ,” says Roodt .
EXTINCTION OF THE FIRE
Roodt explains that to stop a combustion reaction , one of the three elements of the fire-triangle ( heat , fuel and oxygen ) has to be removed . “ Without sufficient heat , a
|
Image by Evening _ tao on Freepik
A fire suppression system in a parking lot .
fire cannot begin , and it cannot continue . Heat can be removed by the application of a substance which reduces the amount of heat available to the fire reaction . This is often water , which absorbs heat for a phase change from water to steam . Introducing sufficient quantities and types of powder or gas in the flame reduces the amount of heat available for the fire reaction in the same manner . Scraping embers from a burning structure also removes the heat source . Turning off the electricity in an electrical fire removes the ignition source . Without fuel , a fire will stop . Fuel can be removed naturally , as where the fire has consumed all the burnable fuel , or manually , by mechanically or chemically removing the fuel from the fire .
The fire stops because a lower concentration of fuel vapor in the flame leads to a decrease in energy release and a lower temperature . Removing the fuel thereby decreases the heat .
“ Without sufficient oxygen , a fire cannot begin and it cannot continue . With a decreased oxygen concentration , the
|
combustion process slows . Oxygen can be denied to a fire using a carbon dioxide fire extinguisher , a fire blanket or water .”
ROLE OF WATER IN FIREFIGHTING
“ Water can have two different roles . In the case of a solid combustible , the solid fuel produces pyrolysing products under the influence of heat , commonly radiation . This process is halted by the application of water , since water is more easily evaporated than the fuel is pyrolysed . Thereby energy is removed from the fuel surface , and it is cooled , and the pyrolysis is stopped , removing the fuel supply to the flames . In firefighting , this is referred to as surface cooling .
“ In the gas phase , that is in the flames or in the smoke , the combustible cannot be separated from the oxidiser , and the only possible action consists of cooling down . In this case , water droplets are evaporated in the gas phase , thereby lowering the temperature and adding water vapour making the gas mixture non-combustible . This requires droplets of a size less than
|
about 0.2 mm . In firefighting , this is referred to as gas cooling or smoke cooling ,” says Roodt .
“ Cases also exist where the ignition factor is not the activation energy . For example , a smoke explosion is a violent combustion of unburned gases contained in the smoke created by a sudden fresh air input ( oxidiser input ). The interval in which an air andgas mix can burn is limited by the explosive limits of the air . This interval can be very small ( kerosene ) or large ( acetylene ).”
He notes that water cannot be used on certain type of fires :
• Fires where live electricity is present – as water conducts electricity it presents an electrocution hazard .
• Hydrocarbon fires – as it will only spread the fire because of the difference in density and hydrophobicity . For example , adding water to a fire with an oil source will cause the oil to spread , since oil and water do not mix .
• Metal fires – as these fires produce huge amounts of energy ( up to 7.550 calories per kilogram [ a figure which is sometimes disputed ] for aluminium ) and water can also create violent chemical reactions with burning metal ( possibly even serving as an additional oxidising agent ).
“ Since these reactions are well understood , it has been possible to create specific water additives which will allow a better heat absorption with a higher density than water , carrying free radical catchers on the fire , carrying foaming agents to enable water to stay on the surface of a liquid fire and prevent gas release , and carrying specific reactives which will react and change the nature of the burning material .”
Water additives are generally designed to be effective on several categories of fires ( class A + class B or even class A + class B + class F ), meaning a better global performance and usability of a single extinguisher on many different types of fires ( or fires that involve several different classes of materials ).
|
|
|
PASSIVE VS ACTIVE FIRE PROTECTION
Roodt describes Passive Fire Protection ( PFP ) as a group of systems that compartmentalise a building through the use of fire-resistance rated walls and floors . “ Compartmentalising your building into smaller sections helps to slow or prevent the spread of fire or smoke from one room to the next . PFP helps to limit the amount of damage done to a building and provides its occupants more time for evacuation . PFP includes fire and smoke
|