2006 Muttrah Incident Report - authority for electricity regulation, oman

8 SITE SAFETY
8.1 Use of Limitation of Access
As indicated in Section 6 above the work at Muttrah substation was being carried out
under a Limitation of Access issued by a duly authorised engineer of MEDC. According
to the Safety Rules of the MHEW (the Rules currently in force in MEDC) a Limitation of
Access is a form issued and cancelled by a Senior Authorised Person or Authorised
Person specifically authorised to do so, defining the limits and nature of work which may
be carried out in the vicinity of Live apparatus.
Under normal circumstances the use of a Limitation of Access (rather than a Permit to
Work or Sanction for Test) for the work being carried out at Muttrah was perfectly
acceptable. The racking in/out of OCB/trucks with the busbar and feeder alive is
common practice and does not normally require even a Limitation of Access. However in
the particular circumstances of the incident the VCB/trucks were actually being adjusted
to fit and tested in a Brush cubicle for the first time. The use of a Permit to Work (with the
busbar and feeder spouts dead) would have been more appropriate. It should be noted
that the incident could still have occurred once the busbar and feeders were made alive
following cancellation of the Permit to Work because of the design defects noted in this
report.
In their report on the incident MEDC state that verbal instructions were given to the ABB
Arab technicians that they were to carry out all adjustments of the trucks in the rackedout
position and that they should inform MEDC when they were ready to rack-in the
breakers. ABB Arab has disputed that these instructions were ever given. Any additional
instructions to be given in respect of a Limitation of Access, for example, should be
written on the Limitation. Having said that, the inquiry believes that the presence or not
of MEDC engineers is irrelevant; the design defects would have manifested themselves
whenever the breaker was racked into the service position.
8.2 Conclusions – Site Safety
In respect of site safety precautions the inquiry concludes:
• That the use of a Limitation of Access was not appropriate given that the VCB/trucks
had never been tested in a Brush cubicle; and
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