The smoke you do not see
In a building fire, most people do not die from flames. They die from smoke and poisonous fumes. Cable runs through ceilings and risers, so a fire can use it as a path from room to room.
The choice of cable jacket can make a fire smaller and the smoke safer. It costs a little more and saves lives.
Key words
| Word | What it means |
|---|---|
| Plenum | a space above a ceiling or under a floor where air moves around a building |
| Fire-rated cable | cable made to burn less and give off less smoke and fumes |
| LSZH | low smoke zero halogen: a jacket that gives little smoke and no harmful halogen gas |
| Toxicity | how poisonous something is |
| CPR | the Construction Products Regulation, which sets fire classes for cable fixed in buildings |
| Declaration of performance | a maker's paper that states a cable's fire class |
| Fire-resistant | able to keep working for a set time in a fire |
| PVC | a common cheap plastic used for ordinary cable jackets |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can say why fire-rated cable is safer than ordinary cable, and name the rule that governs it in the UK.
Starter: cable and the specification
Have a go
Starter: cable and the specification
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Ordinary cable in a fire
Ordinary cable has a PVC jacket. In a fire, PVC burns and gives off thick black smoke and acid fumes. Smoke hides the exit signs. The acid harms lungs and damages equipment far from the fire.
The jacket also melts and drips, which can spread the fire.
Ordinary cable and fire-rated cable
| Feature | Ordinary PVC cable | Fire-rated cable |
|---|---|---|
| Toxic fumes | More | Lower toxicity |
| Smoke | Thick and dark | Lower smoke |
| Burning | Burns and spreads flame | Reduced burning |
| Material breakdown | Melts and drips | Reduced breakdown |
| Heat | Fails at lower heat | Copes with higher heat |
| Rules | May not meet the rules for the building | Made to meet the CPR class asked for |
The cells students fill in are left blank in this preview.
Plenum, LSZH and CPR
Plenum is an American word. A plenum is the air space above a ceiling. In the USA, cable allowed there is called plenum-rated.
In the UK and Europe, the matching idea is LSZH cable and a fire class under the CPR. A cable fixed in a building has a class and a declaration of performance.
Check: fire and cable
Have a go
Check: fire and cable
4 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.