Which of the following method is used to make the timber fire resistance?
Making Timber Fire-Resistant
While timber cannot be made completely fire-proof, its resistance to ignition and combustion can be significantly improved through chemical treatments. These treatments work by creating a protective barrier or by releasing non-combustible gases when heated, thus slowing the spread of fire. This is a separate goal from preservation, which protects against biological threats.
📝 Detailed Analysis of the Options
(a) Coating with tar paint
Tar is a combustible, organic material. Coating wood with tar is a method of preservation used to make it water-resistant, but it will actually increase its flammability rather than making it fire-resistant.
(b) Pumping creosote oil into timber at high pressure
This describes the Bethel process, a method of preservation against rot and insects. Creosote is a highly effective preservative, but it is also an oil distilled from coal tar and is combustible. It does not provide fire resistance.
(c) Seasoning process
Seasoning is the process of drying wood to reduce its moisture content. While dry wood is necessary for any treatment to be effective, seasoning itself does not make the timber fire-resistant. In fact, dry wood ignites more easily than wet wood.
(d) Soaking it in ammonium sulphate
This is the correct answer. Ammonium sulphate is a well-known fire-retardant chemical. When heated, it releases non-flammable gases (like ammonia and water vapor) that dilute the flammable gases produced by the wood, effectively smothering the combustion process. Soaking timber in a solution of such salts is a common method to impart fire resistance. Other chemicals used for this purpose include borax, boric acid, and various phosphates.
📊 Timber Treatments and Their Purpose
| Treatment | Primary Purpose | Combustibility |
|---|---|---|
| Soaking in Ammonium Sulphate | Fire Resistance | Reduces Flammability |
| Coating with Tar | Preservation (Waterproofing) | Increases Flammability |
| Pressure treating with Creosote | Preservation (Anti-rot/insect) | Combustible |
| Seasoning | Drying / Stability | Makes wood easier to ignite |
💡 Study Tips
- Chemical Salts for Fire: Remember that inorganic salts like sulphates, phosphates, and borates are used for fire resistance.
- Oils and Tars for Preservation: Oily or tarry substances like creosote and tar are generally used for preservation against water and rot, and they are typically flammable.
- Distinguish the Goal: Always ask: is the goal to stop fire, or to stop rot and bugs? The answer determines the correct treatment method.