What is the difference between counterflow and concurrent flame spread?

The distinction between counterflow and concurrent flame spread revolves around the direction of the flame spread relative to the air or smoke movement in the environment. Counterflow flame spread occurs when the fire spreads in the opposite direction to the prevailing airflow, effectively allowing the flames to encounter a continuous supply of oxygen, which can enhance combustion. This situation is commonly observed in environments such as vertical shafts or chimneys, where the direction of the flames is opposite to that of the air movement.

In contrast, concurrent flame spread occurs when fire spreads in the same direction as the airflow. This scenario can lead to a reduction in the effective combustion due to the reduced availability of oxygen as the fire moves forward, away from its source of air.

Understanding these two concepts is crucial for fire investigators and safety professionals to assess fire behavior, predict the movement of flames, and develop effective fire suppression strategies.