Start with the fire risk. Water extinguishers suit Class A materials such as wood, paper, cloth and packaging. AFFF foam works on Class A and also on Class B flammable liquids such as petrol, diesel, solvents and paint, because the foam spreads a film over the liquid and stops vapour from re-igniting. Neither type should be used on live electrical equipment.
Then pick the operation type. Stored pressure units keep nitrogen inside the same cylinder as the agent and have a pressure gauge you can read at a glance. Cartridge operated units hold the CO2 in a separate cartridge (to IS 4947) that is pierced when you operate the unit, which many industrial users prefer because refilling is simple on site.
Choose the series and body next. RQ series units have a mild steel body with internal plastic lining and external pure polyester powder coating. HQ series units add a stainless steel body, unique gauge testing system, helium leak testing and CE marking along with BIS approval to IS 15683:2006.
For large liquid fire risks such as refineries, tank farms and paint shops, use the 45 Ltr or 60 Ltr trolley mounted AR-AFFF foam unit with its 20A:233B rating and 9 m throw. For general office and shop cover, 6 Ltr or 9 Ltr portables mounted near exits are usually enough. Call FPS if you want help matching quantity and placement to your floor plan.