What is the minimum total capacity of dry powder fire extinguishers required on an ADR transport unit with a maximum permissible mass of more than 7.5 tonnes?

1. 12 kg, with at least one extinguisher having a minimum capacity of 6 kg
2. 8 kg, with at least one extinguisher having a minimum capacity of 2 kg
3. 4 kg, with at least one extinguisher having a minimum capacity of 2 kg
4. 20 kg, with at least one extinguisher having a minimum capacity of 9 kg