In the Hazard Identification Number (HIN) displayed on the top half of an orange plate, what does a doubling of a number (such as 33 or 88) indicate?

1. The substance has secondary hazards of the same class
2. An intensification of that particular hazard (e.g., highly flammable or highly corrosive)
3. The vehicle is carrying two separate compartments of the same substance
4. The substance is a polymerizing compound requiring temperature controls