Start with size. Portable CO2 units are offered in 2 kg, 3 kg and 4.5 kg by most of these brands, Balaji Fire Safety lists 4 kg and 4.5 kg, and Ceasefire also lists 5 kg in its EN approved range. For electrical rooms, transformer areas and larger plant, choose a trolley or wheeled unit: 6.5 kg, 9 kg and 22.5 kg sizes are offered by Kanex, Minimax and Savemax (the Savemax 22.5 kg is a twin cylinder trolley), Balaji Fire Safety lists a 9 kg trolley, Ceasefire lists 6.5 kg and 22.5 kg plus a 20 kg EN approved unit, and trolley units give a longer discharge and more reach than portable ones.
Next read the fire rating on each model. CO2 carries a B rating only, for flammable liquids, and the figure depends on size and the standard it is tested to: 2 kg units are listed at 21B, 34B or 13 B depending on the model, and the first trolley size of several ranges is listed at 55B. Balaji Fire Safety lists 55B on both its portable and 9 kg trolley units, with a discharge time of more than 20 sec on the trolley. Minimax, for example, lists a minimum effective discharge of 8 seconds for its 2 kg steel unit and 20 seconds for its 6.5 kg mobile unit.
Then choose the cylinder and valve. Steel cylinders are the usual choice, and Balaji Fire Safety lists a manganese steel cylinder on its 9 kg trolley; aluminium bodies from Kanex (HQ series), Minimax (grade 6061, designed as per IS 15660:2017) and Ceasefire (EN range) weigh less, and Minimax states up to 30 percent lighter than a seamless steel cylinder with corrosion resistance for coastal and high salinity areas. Squeeze grip valves, as on the Balaji Fire Safety units, work with one hand, while the Kanex wheel type valve is turned open by hand.
Finally match approvals to your NOC or tender. Ceasefire lists IS 15683 for its 2 kg and 4.5 kg BIS models and IS 16018 for its 6.5 kg and 22.5 kg models, both with PED; Kanex lists IS 2878:2004 for portable units and IS 16018: 2012 for trolley units, with CE and CCOE/PESO; Minimax units are ISI marked; Savemax units are BIS/ISI marked and CPWD approved; and Balaji Fire Safety lists ISI, BIS, ISO and CE for its portable units and ISI for its 9 kg trolley. Kartar Valves publishes no capacities for its CO2 unit, so FPS confirms the size on enquiry.