Firefighters swapped their breathing apparatus for soap and sponges at a charity car wash in Potters Bar on Saturday.
The crew raised more than £150 at the Mutton Lane station by offering to spruce up passing motors.
All donations will be handed to The Firefighters Charity, which provides help and support for injured servicemen.
Crew Commander Ross Henderson said: “The guys are always keen to do their bit and showed their dedication on Saturday when they took part despite being on duty.
“Fortunately we weren’t called out so we managed to get a steady flow of cars coming through. We’ve obviously aware of the work the charity does and it is important that we support it.”