Health and Safety Executive INDUSTRIAL RADIOGRAPHY ACCIDENT IN THE UK David Orr H M Specialist...
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Transcript of Health and Safety Executive INDUSTRIAL RADIOGRAPHY ACCIDENT IN THE UK David Orr H M Specialist...
Health and Safety Executive
INDUSTRIAL RADIOGRAPHY ACCIDENT IN THE UK
David Orr
H M Specialist Inspector of Health and Safety (Radiation)
Health and Safety Executive
Health and Safety Executive
Industrial radiography accidents/incidents in UK:• Approx 10 per annum but very rare that doses
received > dose limit• Vast majority relate to detached gamma source• Last 2 major accidents (doses > dose limit) happened
in radiography enclosures.• Main failings:
• Poor risk assessment• Poor contingency plans; not properly rehearsed• Too much reliance on RPA
Health and Safety Executive
Accident with Yb-169 radioactive source:• Radiographers didn’t understand nature of source• Yb-169 used (rare in UK) instead of more usual Ir-192• Dose rate from Yb-169 source much lower:
• 740 GBq Ir-192 - 2100 μSv/h @ 1m• 85 GBq Yb-169 - 90 μSv/h @ 1m
• Energy of Yb-169 gamma much lower and much more easily shielded• 10th value thickness
• 12 mm lead for Ir-192• 2 mm lead for Yb-169
Health and Safety Executive
Radiographers didn’t understand source design/construction:
Special form source (capsule only)• Source capsule “screwed and glued” in
position• Source capsule not welded to holder to
allow for low gamma energy• Very different to normal Ir-192 “pigtail”
Health and Safety Executive
Radiographers didn’t understand design of source:
Health and Safety Executive
• Work was being carried out in enclosure/clean room on large metal component
• Enclosure safety features –• Shielding OK• Automatic wind-out interlocked to access door• Fail to safety warning lights• Gamma alarm inside enclosure but had to be
switched on separately to other systems• Due to low energy of source gamma alarm could not
detect detached/lost source inside component
Health and Safety Executive
Health and Safety Executive
Health and Safety Executive
Health and Safety Executive
Access for guide tube was difficult:• Required use of bends tighter than manufacturer’s
recommendations• Some examinations required use of manual wind-out
as automatic wind-out unable to deploy source.• Many of safety features not operational with manual
wind-out• Bespoke guide tube designed with open ended snout
to facilitate better images and prevent “contamination” of component
Health and Safety Executive
Health and Safety Executive
Techops 880 container being used:
• One of standard source containers in UK
• Good safety features
• Radiographers were unaware that dose rate on outside of container was the same whether or not source was present
Health and Safety Executive
Techops 880 container used
Health and Safety Executive
What happened ?
• Radiography being carried out with manual wind-out
• Gamma alarm was not switched on• Unknown to radiographers, source glue had
broken• Torsional forces applied to source capsule
when driven around steep bend causing source capsule to unscrew
Health and Safety Executive
• Last radiograph of the day - source fell out of open ended guide tube into component.
• Presence of lost source not detected by gamma alarm
• Radiographer retracted source – positive indication on source container that source was “home”
• Monitoring of source container “indicated” that source was present
Health and Safety Executive
• Radiographer left for evening and component wheeled from enclosure to clean room
• Welders arrived and carried out next welds
• At end of shift spotted “source” inside component – looked like small screw
• Source removed and passed amongst welders
Health and Safety Executive
• Radiographers returned for next shift - EPDs alarmed on approaching source (set to alarm at 100 μSv/h)
• Alarms ignored – assumed battery was low• Radiographers handled source• Finally radiation monitor switched on and
presence of source identified• Source recovery plan put in place
Health and Safety Executive
Consequences:• Several welders and radiographer received hand doses above
dose limit but no deterministic effects observed• Whole body doses increased but below dose limit• Dose consequences could have been much much worse• IN served for inadequate risk assessment
• Nature of source• Suitability of warning/safety devices• Use of bespoke equipment
Company to be prosecuted in Crown Court