Interaction of Heat and Steam in Firefighting: Learn about steam expansion, water application, and firefighter safety.
When dealing with fires, it’s essential to know how much water to apply and its effects. Incorrect application can lead to negative consequences.
Firstly, it’s crucial to recognize the expansion rate of steam. One liter of water converts to 1,700 liters of steam. This means that water, when heated and turned into steam, expands 1,700 times its original volume.
By applying a small amount of water, you can limit the amount of steam produced. This helps maintain the heat layer and cool both the gas and surfaces by removing heat energy.
However, applying too much water can produce excessive steam, disrupt the heat balance, and reduce visibility. It can also affect personal protective equipment (PPE) and firefighting gear. Note that steam not mixed with fire gases is colorless and as transparent as air. As steam descends, it affects the fresh air layer near the floor. Firefighters need to maintain the heat balance, ensuring fresh air and visibility are preserved during operations.
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The Impact of Steam on Firefighters
Steam molecules are much smaller than the pores in the skin. This means steam can penetrate through firefighting gear and reach the skin, potentially causing burns. When steam contacts the dermis, the stored heat energy condenses directly on the skin, causing burns.
Optimal Water Application
The recommended approach for internal water application is to use a small amount of straight stream. This limits steam production and air entrainment, allowing for effective cooling of the space. Adjust the water flow based on the burning area and the rate of combustion.
Superheated Steam
Superheated steam is steam heated above its boiling point of 100°C. Applying water to a fire produces large amounts of superheated steam. Careless water application can lead to injuries due to steam burns. Superheated steam can exceed 200°C, capable of igniting materials like paper. This principle is used in kitchen appliances like steam ovens, which cook food by “baking” it at over 300°C. Firefighting gear alone cannot protect against such extreme conditions, which is why fire hoods are mandatory in many countries.
Steam Explosions
A steam explosion occurs when water comes into contact with a very hot substance, rapidly vaporizing and expanding. This phenomenon is similar to water droplets violently bouncing off a hot frying pan. Water expands about 1,700 times when it turns into steam, causing a sudden increase in volume and resulting in an explosion.
Risks of Steam Expansion
The expansion of steam can cause overpressure, potentially burning trapped individuals. The conversion of water to steam absorbs significant heat (539 kilocalories per kilogram of steam). This process, known as “steam expansion,” displaces oxygen in a burning room, achieving both suffocation and extinguishment effects. However, the negative effect is that steam expansion can generate pressure, moving hot gases elsewhere and endangering trapped individuals.
By understanding these principles, firefighters can better manage water application to effectively combat fires while minimizing risks.
Reference page: Fire Fighting skills are crucial, and everyone must improve them.
References National Fire Protection Association (NFPA)
