The incident occurred on a Saturday , while the site maintenance staff were working overtime . The building ’ s emergency exit had been left open to access the temporary working area while staff carrying out the drain repair moved in and out . Maintenance to the building ventilation was carried out on alternate Saturdays , and this was a “ maintenance weekend ”. The maintenance included switching off the building air intake ( plenum ) and extract systems while they were worked on . That work was carried out under a System of Work .

When maintenance staff working on the ventilation system had completed their work , they decided to switch the ventilation back on . To maintain the depression in air pressure in the building , the practice was to switch on the extract first and check this was functioning correctly before switching on the plenum .

With the extract running but no plenum to balance the air , the reduction in air pressure was so great that it sucked the tent into the building , bending the frame and leaving the contaminated drain exposed to the external atmosphere .

Fortunately , plenty of people were on site to respond and cover the contaminated area . No contamination was released to the environment , and the tent was safely repaired and reinstalled .

Lesson learned – make sure that when a Permit to Work is drawn up , everyone likely to be affected is consulted , and the impact of any other work is considered .

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Hazardous area

Permit to work must be obtained

Radiation Protection Today Winter 2021 29