Thugs hurled a metal wheel brace at a fire engine as it raced to answer a 999 call.
The missile smashed the fire truck's windscreen and showered the crew with glass.
Pieces of glass came within inches of the driver's eyes but no one was seriously hurt.
The engine was unable to continue to the fire call at a disused hospital in New Church Road, Hove, on Friday evening.
A second crew attended and found the fire was out. Vandals had put lighted paper through a letterbox but security staff had extinguished the flames.
A brigade spokesman said: "The attack on a fire tender put not only the lives of the crew at risk but also potential fire victims.
"It delayed our response and that could have stopped us reaching people in need."
The attack happened in Sackville Road, Hove, at 9.30pm. The missile was thrown from a dark blue car as it sped past at 50 mph.
Police are trying to trace the occupants and appealed for anyone with information to come forward.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article