The safe isolation of plant and equipment (HSG253) - Health and ...
The safe isolation of plant and equipment (HSG253) - Health and ...
The safe isolation of plant and equipment (HSG253) - Health and ...
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<strong>Health</strong> <strong>and</strong> Safety<br />
Executive<br />
An example<br />
Production operators were carrying out maintenance on a filter. <strong>The</strong> pump serving<br />
the filter was isolated only via s<strong>of</strong>tware – <strong>and</strong> a dem<strong>and</strong> signal from the <strong>plant</strong><br />
overrode the pump de-selection. A ball valve between the pump <strong>and</strong> the filter<br />
was closed, but may have been passing. A joint in the plastic pipeline failed. <strong>The</strong><br />
operators were sprayed with sodium hypochlorite.<br />
All <strong>equipment</strong> within the <strong>isolation</strong> boundary should be de-energised so that<br />
control signals do not affect the integrity <strong>of</strong> the <strong>isolation</strong>. <strong>The</strong> isolating valve<br />
should be tested <strong>and</strong> secured. Disconnections <strong>of</strong> motive power should be<br />
recorded <strong>and</strong> checked-<strong>of</strong>f during reinstatement.<br />
192 You should identify by risk assessment whether procedural or PTW control is<br />
appropriate for own <strong>isolation</strong>s.<br />
193 Where own <strong>isolation</strong>s are carried out under procedural control, st<strong>and</strong>ardisation<br />
<strong>of</strong> <strong>equipment</strong> (<strong>plant</strong> design) is particularly important.<br />
194 Where the consequences <strong>of</strong> error in applying the procedural controls could be<br />
<strong>safe</strong>ty critical, activities should be controlled by PTW. Work which affects process<br />
control <strong>and</strong>/or <strong>safe</strong>ty systems (eg involves removal <strong>of</strong> process indication, control,<br />
alarm or trip functions) should always be carried out under PTW. Work control by<br />
procedure is also inappropriate where a task cannot be fully defined. Remember<br />
that no person should issue a permit for their own activity. 10<br />
195 Own <strong>isolation</strong>s require that:<br />
■<br />
■<br />
■<br />
■<br />
■<br />
<strong>isolation</strong>, intrusive work <strong>and</strong> reinstatement are carried out by the same person;<br />
that person is competent to perform the <strong>isolation</strong>, to undertake the task <strong>and</strong> to<br />
reinstate the <strong>equipment</strong>;<br />
the <strong>isolation</strong> is under the control <strong>of</strong> the competent person, who is continuously<br />
present at the worksite while the pressure envelope is breached;<br />
the <strong>isolation</strong> points are identified <strong>and</strong> secured unless they are all within sight/<br />
reach <strong>of</strong> the ‘own-isolator’ (who must then remain in attendance for the<br />
duration <strong>of</strong> the work); <strong>and</strong><br />
communication with any appropriate control room or operating unit (eg by<br />
radio) is available throughout the task.<br />
196 In addition, for own <strong>isolation</strong>s performed by competent instrument technicians:<br />
■<br />
■<br />
■<br />
the permit-to-work will identify any potential residual risks <strong>and</strong> specify the<br />
appropriate control measures, including mitigation measures in case <strong>of</strong> loss <strong>of</strong><br />
containment;<br />
relevant control room operators should be involved in PTW authorisation for<br />
work on systems which impact on <strong>safe</strong> control <strong>of</strong> the <strong>plant</strong> eg instrumented<br />
<strong>safe</strong>ty-related functions <strong>and</strong> many process control functions; <strong>and</strong><br />
independent checking <strong>of</strong> reinstatement is necessary where failure to reopen<br />
an <strong>isolation</strong> valve after completion <strong>of</strong> instrument work might defeat a <strong>safe</strong>tyrelated<br />
function, <strong>and</strong> this may not be self-revealing.<br />
<strong>The</strong> <strong>safe</strong> <strong>isolation</strong> <strong>of</strong> <strong>plant</strong> <strong>and</strong> <strong>equipment</strong> Page 40 <strong>of</strong> 81