fire detection and suppression
introduction
A fire can wipe out all my hard work. I need a fire detection system and a way of dealing with electrical fires.
I have a cheap battery operated fire alarm for fire detection. For fire suppression I have a fire blanket and a fire extinguisher.
what it is
Computer room fire suppression is essential. When an organisation builds a data center it spends lots of money on fire protection systems. Fires can be detected with HSSD (High Sensitivity Smoke Detection) systems and smart smoke detection systems. An HSSD system may use lasers and be a thousand times more sensitive than a point smoke detector. They can be extinguished by flooding a room with inert gas (such as a Halon alternative or carbon dioxide), dry chemicals or water.
Some organisations do the legal minimum, such as installing automatic sprinkler systems. Since water conducts electricity, surely this can lead to fried employees.
In the olden days electronics were protected by halon gas fire extinguishing systems. Halon is bad for the ozone layer and these systems can no longer be purchased.
| LIC topography: fire detection and suppression | ||
|---|---|---|
| fire alarm | fire blanket | fire extinguisher |
 |
 |
 |
Knowing how to suppress a fire means knowing a little about fires. Fires are divided into four classes. I think fire classes might be like shoe sizes: they vary from country to country.
| LIC table: fire classes | ||
|---|---|---|
| class | for | description |
|
A
|
ordinary combustible materials such as paper, wood, cardboard, and most plastics | The numerical rating on these types of extinguishers indicates the amount of water it holds and the amount of fire it can extinguish. |
|
B
|
flammable or combustible liquids such as gasoline, kerosene, grease and oil | The numerical rating for class B extinguishers indicates the approximate number of square feet of fire it can extinguish. |
|
C
|
electrical equipment, such as appliances, wiring, circuit breakers and outlets | Never use water to extinguish class C fires - the risk of electrical shock is far too great! Class C extinguishers do not have a numerical rating. The C classification means the extinguishing agent is non-conductive. |
|
D
|
combustible metals, such as magnesium, titanium, potassium and sodium | commonly found in a chemical laboratory. These types of extinguishers also have no numerical rating, nor are they given a multi-purpose rating - they are designed for class D fires only. |
a fire alarm
For fire detection I use a cheap battery operated smoke detector and hope I am nearby if the alarm goes off.
a fire blanket
The fire blanket will do for smothering small stuff. Fire blankets are covered by British Standard BS 6575.
a fire extinguisher
There are three common types of fire extinguisher. They are not exactly matched with the three classes of fire.
| LIC table: fire extinguisher types | ||
|---|---|---|
| type | for fire class | description |
| water | A | Never use a water extinguisher on grease fires, electrical fires or class D fires - the flames will spread and make the fire bigger! Water extinguishers are filled with water and pressurized with oxygen. Again - water extinguishers can be very dangerous in the wrong type of situation. Only fight the fire if you're certain it contains ordinary combustible materials only. |
| dry chemical | BC | standard dry chemical extinguisher. It is filled with sodium bicarbonate or potassium bicarbonate. The BC variety leaves a mildly corrosive residue which must be cleaned immediately to prevent any damage to materials. |
| dry chemical | ABC | multipurpose dry chemical extinguisher. The ABC type is filled with monoammonium phosphate, a yellow powder that leaves a sticky residue that may be damaging to electrical appliances such as a computer |
| carbon dioxide (CO2) | BC |
CO2 extinguishers are highly pressurized. The pressure is so great that it is not uncommon for bits of dry ice to shoot out the nozzle. CO2 extinguishers have an advantage over dry chemical extinguishers since they don't leave a harmful residue - a good choice for an electrical fire on a computer or other favorite electronic device such as a stereo or TV. They don't work very well on class A fires because they may not be able to displace enough oxygen to put the fire out, causing it to re-ignite. |
Fire extinguishers are also color coded. They are usually solid red with a big label stuck on them. The label has a band of color at the top.
| LIC table: fire extinguisher colors | |
|---|---|
| color | description |
| Red with Blue Zone | dry powder (standard or multi-purpose) |
| Red | water |
| Red with Yellow Zone | AFFF (Aqueous Film-Forming Foam). Multi Purpose. |
| Red with Black Zone | CO2 (carbon dioxide) |
Fire extinguishers are sold in different sizes. There are titchy 1 kilogram ones for little workshop fires and fat 15kg ones for putting out moon rockets. The bigger the extinguisher the more seconds it will work. A 1kg multi-purpose powder fire extinguisher may only give ten seconds of discharge. It will successfully manage to make a mess in those ten seconds.
A fire extinguisher needs to be maintained. I may need to check mine at service intervals or replace it at the end of its lifetime. It has a cartridge which may leak. It has no gauge to break. It contains powder that can transform into a bug clump of uselessness.
my shed
My shed is a fire hazard because it is made from wood. My computers have electricity coursing through them so they are also fire hazards. Since my computers have electricity coursing through them I need to worry about class C fires. Since my shed is made from wood I also need to worry about class A fires.
I made sure I can get away from a shed fire by not placing fire hazards (the computers) between me and my emergency exit (the shed door).
I can attempt to put out a small fire. I follow these instructions.
- Turn off all electricity using the consumer unit.
- Suppress the fire.
If the fire is dangerous (eg. it's big and it makes me want to go to the toilet) I don't attempt to put it out.
- Get everyone away from the fire.
- Phone the fire brigade, the only people properly equipped to deal with fires.
