What is the correct interpretation of a Class 1 tunnel restriction code such as "B1000C"?

1. Passage is prohibited in B tunnels if net explosive mass exceeds 1000 kg; otherwise prohibited in C, D, and E tunnels
2. The vehicle must be driven at less than 10 km/h through B and C tunnels
3. The vehicle is prohibited in B tunnels for 1000 meters, then permitted in C tunnels
4. The transport unit must carry 1000 kg of water for fire suppression