This 2nd pattern West Sussex Fire Brigade helmet transfer is the post 1974 design with the badge which came into force after the 1974 Fire Services Act. 
It is a water slide helmet transfer & is applied to the front of the fire helmet by soaking in water for a few minutes, peeled from the backing paper & applied to the front of the fire helmet by gently dabbing dry with a soft towel. The transfers had a water based adhesive which allowed them to stick after the transfer was applied & suitable for operational fire helmets. 
Helmet transfers are far more delicate than metal cap badges & over time will be very collectable. 
A great unused helmet transfer from the 1974 West Sussex Fire Brigade to add to any fire brigade transfer collection.