When using water mist as an extinguishing mechanism, the effectiveness of a fine mist depends on

When using water mist as an extinguishing mechanism, the effectiveness of a fine mist depends on
A . the ability of the mist to directly spray on the fire.
B . how much mist diverts to the compartment boundaries.
C . how much conductive heat the mist system will absorb.
D . the momentum and direction of the spray relative to the fire.

View Answer

Answer: D

Explanation:

When using water mist as an extinguishing mechanism, the effectiveness of a fine mist depends on the momentum and direction of the spray relative to the fire. The momentum and direction of the spray determine how well the mist can penetrate the fire plume and reach the flame zone, where the mist droplets can evaporate and cool the fire, displace oxygen, and dilute the fuel vapors. The mist spray should have sufficient momentum to overcome the buoyancy and entrainment of the fire plume, and the direction of the spray should be aligned with the fire plume to avoid deflection and dispersion. The ability of the mist to directly spray on the fire, how much mist diverts to the compartment boundaries, and how much conductive heat the mist system will absorb are not the main factors affecting the extinguishing effectiveness of a fine mist.

References: Water Mist Systems Overview | NFPA; Engineering Relations for Water Mist Fire Suppression Systems; Effectiveness of Swirl Water Mist Nozzles for Fire Suppression