Convection is the process of heat transfer through the movement of fluids (such as air or water) due to differences in temperature. In the context of a fire, hot gases and smoke are generated, which are significantly hotter than the ambient air. These hot gases and smoke rise due to their lower density compared to the cooler air around them. This movement of hot gases upwards is an example of convection.
When a person is trapped in a burning building, the situation becomes critical. The air near the ceiling is usually much hotter and filled with toxic gases and smoke, making it extremely hazardous for breathing and general well-being. This is where the principle of convection comes into play.
By getting low and crawling, you are taking advantage of the fact that hot gases rise and accumulate near the ceiling. By staying close to the ground, you can access air that is relatively cooler and contains fewer toxic fumes.
Here's how it works:
Cooler Air at Lower Levels: As hot gases rise, they create a temperature gradient within the room. The air near the floor tends to be cooler because heat rises. This cooler air is easier to breathe and provides better visibility.
Avoiding Toxic Gases: Toxic gases and smoke tend to concentrate near the ceiling where the fire is actively burning. Staying low reduces your exposure to these harmful substances, increasing your chances of survival.
Path to Safety: Crawling along the floor helps you stay under the layer of hot gases, making it easier to see and breathe. It also allows you to identify exit routes more effectively.
Temperature Difference: The temperature difference between the hot gases near the ceiling and the cooler air near the floor creates a convective flow. Air moves from cooler regions to warmer regions, helping to carry smoke and heat away from your immediate vicinity.