Dry chemical powder is discharged from an extinguisher or a fixed installation as a free-flowing cloud.

It is most effective for:

• Initial control of fires from oil or chemical spills on a jetty or tanker deck.
• Fires in confined spaces.
• Burning liquids escaping from leaking pipelines and joints.

Key characteristics:

• It is a non-conductor, making it suitable for electrical fires.
• It must be directed into the flames.
• It has negligible cooling effect and provides no protection against re-ignition (e.g., from hot metal surfaces).
• Certain types can break down a foam blanket; only “foam compatible” types should be used with foam.
• Powder clogs and becomes useless if it becomes damp during storage or filling.

Piping Arrangements for DCP Fire-Fighting Systems on Chemical Tankers A fire-extinguishing unit with two or more monitors, hand hose lines, or a combination should have:

• Independent pipes (with a manifold at the powder container), unless a suitable alternative means is provided to ensure proper performance.
• Where two or more pipes are attached to a unit, the arrangement must allow any or all monitors and hand hose lines to operate simultaneously or sequentially at their rated capacities.

Where fixed piping is provided between the powder container and a hand hose line or monitor:

• The length of piping should not exceed the length capable of maintaining the powder in a fluidized state during sustained or intermittent use.
• The system must be capable of being purged of powder when shut down.