Re: [foxboro] Locking / Disabling equipment

I agree with the sentiment that only removing energy sources truly locks out
a device, but we practice "defense in depth".  In addition to removing
energy sources, we connect a BOOL block in a special TAGOUT directory to the
start/run logic (typically CALCA blocks or LOGIC blocks) and if this is
TRUE, the visibility of the start button is turned off, a large rectangle
covers the start buttons saying "HOLD" or "TAGGED", and the logic will not
set the start output.  

We further require that to tag out a device in the DCS, an associated STRING
is not empty.  The intent is to fill in the STRING block with a work package
number, technician name, etc. when tagging out the device.  The script
setting the BOOL block checks to see if there is text in the STRING block,
and will not tag it out if there isn't, or if the device is already
energized (some locations don't use that second restriction).  Once tagged
out, the tag clearing script in the DCS clears both the BOOL and the STRING.
We even go so far as to name the BOOL and STRING blocks with names that show
they are associated with each other, and place them in a separate compound
containing only tagout data blocks.  

We also employ similar logic to override logic from bad digital inputs.

Jim Mowrey

-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of Moore, Kenneth, Celanese/US
Sent: Wednesday, August 24, 2005 2:16 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Locking / Disabling equipment

We too use the DISABLE parameter, but to only inform the rest of the
logic that this device is out of service. We still do physical lock out
/ tag out for allOSHA specifications, but I'm not a safety expert.

Ken Moore
Celanese Emulsions
Enoree, SC=20

-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of brad.s.wilson@xxxxxxxxxxxxxx
Sent: Wednesday, August 24, 2005 2:12 PM
To: foxboro@xxxxxxxxxxxxx
Subject: [foxboro] Locking / Disabling equipment

We're wrestling with the best way to lockout equipment operated by the
DCS.
Our policy states that the technician doing the work must ultimately be
in sole control of the locking "device".  The obvious (and advertised)
method to prevent operation of a DCS-controlled device is via the block
DISABLE parameter.  However, anyone with access to SELECT (or any other
way to get block default display) also has access to the DISABLE
parameter.  Our past practice has been to physically lock a motor
starter, disconnect a valve air supply, remove a valve acruator, etc,
rather than rely on the DCS for a secure lockout.

I'd like to know how other users manage lock/tag/try for DCS-controlled
equipment.

Brad Wilson
ExxonMobil Chemical Co
Edison Synthetics Plant
732-321-6115
732-321-6177 fax
Brad.S.Wilson@xxxxxxxxxxxxxx

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