What is admitted to the boiler air casing during a fire in the air casing until the fire is out?

The use of steam smothering during a fire in the boiler air casing is based on steam's ability to displace oxygen, which is crucial for combustion. When steam is introduced, it can help reduce the concentration of oxygen in the vicinity of the fire, thereby limiting its ability to burn. This method is often preferred in certain situations because it can effectively cool the area and suppress the flames without introducing foreign substances that might complicate the boiler operations or leave residues.

In contrast, water mist systems, while useful in various firefighting scenarios, may not be as effective in confined spaces like a boiler air casing where steam is already present and the fire's behavior needs to be managed carefully. Compressed air could potentially exacerbate the situation by supplying more oxygen, thus fueling the fire rather than suppressing it. Similarly, while CO2 is a common fire suppressing agent, its application in a boiler air casing environment may not be ideal due to the operational characteristics required for ensuring safe and effective suppression without affecting boiler performance. Hence, steam smothering stands out as the most effective measure in this context.