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)



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


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


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”


Radiographers didn’t understand design of source:


• 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


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


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


Techops 880 container used


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


• 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


• 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


• 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


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

Health and Safety Executive INDUSTRIAL RADIOGRAPHY ACCIDENT IN THE UK David Orr H M Specialist...

Documents

Transcript of Health and Safety Executive INDUSTRIAL RADIOGRAPHY ACCIDENT IN THE UK David Orr H M Specialist...