BC Dry Chemical Powder (Sodium Bicarbonate) – Standard & Purple-K

BC dry chemical powder is a specialised fire-extinguishing agent designed exclusively for Class B (flammable liquid) and Class C (live electrical) fires. Unlike ABC powder, which contains monoammonium phosphate, the standard BC formulation is built on sodium bicarbonate (NaHCO₃). When discharged into a flame, the heat decomposes the particles, releasing carbon dioxide and water vapour that dilute the oxygen concentration around the fuel surface while simultaneously interrupting the free-radical chain reaction that sustains combustion.

The premium variant, widely known as Purple-K, replaces sodium bicarbonate with potassium bicarbonate (KHCO₃). Purple-K is roughly twice as effective on Class B fires gram-for-gram compared to standard sodium bicarbonate. This makes it the agent of choice for oil refineries, petrochemical tank farms, aircraft hangars, and transformer yards where rapid knock-down of hydrocarbon pool fires is critical. Its distinctive purple tint provides a visible discharge indicator during operations and training.

In Indian fire-service practice, BC powder still holds a strong position in dedicated Class B/C extinguishers installed next to diesel generators, electrical switchgear rooms, flammable-liquid stores, and vehicle workshops. While ABC powder can theoretically cover these scenarios, BC powder delivers a cleaner suppression effect on liquid fires—without the sticky phosphate residue that MAP leaves behind, which can damage sensitive electrical contacts and corrode aluminium surfaces.

Manufacturing involves wet milling of pharmaceutical-grade bicarbonate feedstock, followed by classification to achieve a target particle-size range of 20–40 µm, and surface treatment with zinc stearate or silicone oil to improve free-flow and moisture resistance. The treated powder is then dried to a moisture content below 0.20 %, packaged in moisture-barrier bags, and shipped with a full Certificate of Analysis.

During extinguisher refilling, it is essential to use only the powder type originally specified for the extinguisher model. Mixing ABC and BC powders is a serious quality violation—it alters flow behaviour, can clog siphon tubes, and invalidates the fire rating. Always confirm the extinguisher label and IS plate before selecting the refill agent.

Storage requirements mirror those for ABC powder: sealed bags on raised pallets, relative humidity below 60 %, and a "first in, first out" stock-rotation policy. Purple-K is somewhat more hygroscopic than standard BC, so extra care with climate control pays dividends in service quality.