The speaker discusses the common misconception that water extinguishes fires by blocking oxygen. They explain that water actually works by taking away the heat, thus removing a necessary component of the fire triangle (oxygen, fuel, and heat).
When water is added to a fire, it absorbs a lot of energy from the fire to convert from liquid to steam, thus diverting heat away from the fuel. The speaker notes that the temperature of the average wood fire is between 400-600°C, but water can absorb heat from the fire and convert to steam at 100°C, which is below the ignition temperature of wood (around 150°C).
The speaker also addresses the idea that water might block oxygen from a fire, but notes that this is not a good answer because liquid water can only exist at temperatures below 100°C, which means the fire is already extinguished in that area. Additionally, steam produced from the fire would need to displace a large percentage of the air volume above the fire to extinguish it, which is unlikely unless the fire is in a small, enclosed space.
Here are the key facts extracted from the text:
1. Water is not suitable to put out all fires, such as oil fires or chemical fires.
2. The fire triangle consists of three major requirements for a fire to occur: oxygen, fuel, and heat.
3. To extinguish a fire, at least one of the elements of the fire triangle must be removed.
4. Water extinguishes fires by removing heat, not oxygen.
5. Activation energy is the energy required for a reaction to start.
6. Fire releases energy in the form of heat.
7. Water is non-flammable because it is one of the final products of combustion.
8. The boiling point of water is lower than the temperature of a fire, so it immediately starts boiling when put on a fire.
9. The amount of energy required to convert water from a liquid to a vapor is surprisingly huge.
10. The temperature of an average wood fire is between 400 and 600 C.
11. Wood can ignite at temperatures as low as 150 C.
12. Water absorbs heat from a fire and converts to steam, taking away the heat and preventing the fire from reaching its activation energy.
13. The conversion of liquid water to steam takes place at around 100 C.
14. Fire needs a minimum concentration of 15% oxygen to be maintained, but can still smolder at concentrations as low as 3%.
15. Steam produced from a fire would need to displace at least 90% of the air volume above the fire to totally extinguish it.