Under ADR 4.3.2.2.4, what rule applies to filling tank compartments with liquid dangerous goods to prevent dangerous surge/sloshing movement during transport when tanks are not equipped with surge plates (baffles)?

1. Tanks must be filled exactly to 50% capacity at all times
2. Tanks must never exceed 30% capacity during summer months
3. Tanks over 7,500 L capacity must be filled to more than 80% or less than 20% of their capacity
4. Tanks must be filled to 100% capacity leaving zero outage ullage