This article was reproduced with the kind permission
of the British Broadcasting Corporation
12 November 2007, 18:59 GMT
Fire officials said someone sprayed it through the letterbox of Boots at Cheap Street in Sherborne on Saturday.
About 25 fire and ambulance staff responded and half the street was cordoned off.
Police said it was "mindless criminal damage that has wasted valuable emergency services time and resources".
Station manager Phil Head of Dorset Fire and Rescue Service said it appeared to be a prank that wasted a lot of time and public money, and triggered respiratory problems in three people.
"Both of our appliances from Sherborne attended the scene plus the environmental support unit from Gillingham.
"We then had a call to a property fire also in Sherborne so had to reallocate resources and call in assistance from Somerset's Yeovil appliance as emergency cover.
"The economic impact will also be felt in the town since the high street had to be partly closed while we evacuated the immediate area until we knew what the substance was. "
Dorset Police are investigating.