Around 150 people were evacuated from an NHS blood laboratory in Elstree this afternoon after an air conditioning system caught fire.
Fire crews from Garston, Watford and Borehamwood were called to the NHS Bio Products Laboratory, in Dagger Lane, the largest lab of its type in the country, just before 4pm.
Fire officers from Garston Fire Station's White Watch said their response was "mostly precautionary" and that the incident had been caused by rubber belts in the air conditioning system overheating and filling a first floor room with smoke.
Firefighters had left the scene by 4.40pm.
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