Please see NEW regulations for fire extinguisher  from MSA you can use dry powder

3.2. Hand-held extinguishers 3.2.1. Where a hand-held fire extinguisher is required the vehicle must be equipped with at least one fire extinguisher in compliance with 3.2.2 to 3.2.7 hereunder or with FIA Standard 8865‐2015 (Articles 3.2.2 to 3.2.5 hereunder do not apply in the latter case).

Please note under the new regs the minimum size of handheld AFFF extinguishers will be increased from 1.75 Ltrs to 2.4 Ltrs Existing vehicles competing prior to 1st January 2019 will be ok until 1st January 2022. New build vehicles will have to comply from 1st January 2019

3.2.2. Permitted extinguishants:
AFFF, Clean Agent, powder or any other extinguishant homologated by the FIA.

3.2.3. Minimum quantity of extinguishant: • AFFF 2.4 litres • FireSense 2.4 litres • FX G‐TEC 2.0 kg • Viro3 2.0 kg • Zero 360 2.0 kg • Extreme 2.0 kg • Powder 2.0 kg

3.2.4. All extinguishers must be pressurised according with the manufacturer's instructions. Powder extinguishers must be pressurised to 8 bars minimum, 13.5 bars maximum. Furthermore, each extinguisher must be equipped with a means of checking the pressure of the contents.

3.2.5. The following information must be visible on each extinguisher: • Capacity • Type of extinguishant • Weight or volume of the extinguishant • Date the extinguisher must be checked, which must be no more than two years after either the date of filling or the date of the last check, or corresponding expiry date.

3.2.6. All extinguishers must be adequately protected. Their mountings must be able to withstand a deceleration of 25g. Furthermore, only quick‐release metal fastenings (two minimum), with metal straps, are accepted. Anti‐torpedo tabs are required. It is
prohibited to mount bottles outside the main structure