Belgium Overexposure Incident Provisionally Rated INES Level 4

An investigation is under way into an incident in Belgium
during which an employee at an irradiation sterilisation facility may have
received an energy dose of radiation as high as about 4 Grays (Gy).

The event was provisionally rated as level 4 on the International Nuclear
Event Scale (INES) on 2 April 2006. According to the INES scale, a level 4
rating is an accident without significant off-site risk.

An INES report for the International Atomic Energy Agency said the incident
happened on 11 March 2006 at the Sterigenics facility in Fleurus, Belgium,
but was not reported to the facility’s management until 30 March – after the
employee became seriously ill and then admitted to a specialised hospital on
31 March.

The facility is principally used to sterilise medical devices using gamma
radiation from a sealed cobalt 60 isotope source which is kept inside a
containment vessel. When not in operation, the source is stored in a pool. A
secure hydraulic system removes the source from the pool when it is needed to
irradiate products in a specially designed cell. Safety locks prevent the
removal of the source from the pool when the door of the cell is open.

The INES report said that on 11 March the employee concerned, who has not
been named, went into the room where the cell is situated and noticed that a
gamma monitor alarm system had been activated. The door of the cell was open
and the cell was empty with no irradiation in progress. The employee reset
the monitor alarm system and verified that the alarm did not reactivate. He
then closed the door of the irradiator which, for reasons of safety, required
him to enter and activate a switch at the rear of the cell. This procedure is
designed to ensure that those closing the door can first check that no one is
left inside.

The employee was in the cell for about 20 seconds while performing the check
and he did not notice any anomaly either inside or outside the cell and the
gamma monitor did not reactivate.

Some time after this, the employee suffered nausea and vomiting but did not
consider this might be related to his work. However, nearly three weeks
later, the employee suffered massive hair loss and contacted a doctor. Blood
tests showed that the employee may have been exposed to a dose as high as
about 4 Gy. He was admitted to a French hospital specialising in the
treatment of radiation exposure on 31 March.

The INES report said: “It is provisionally assumed that during his short
presence in the cell, due to a presently not yet identified defect of the
hydraulic system, the source could have been slightly taken out of the pool.
Further investigation is performed in order to check the working of the
hydraulic system and the electrical control system. The specific causes of
the accident are still under investigation.”

It should be noted that a whole-body exposure of 4 Gy is considered serious.
It requires specialised treatment; the prognosis is uncertain without
treatment, but fairly good with treatment.

Zdroj: NucNet

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