OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 15 Managing the Control of Hazardous Energy

Section 215.4 Isolating piping

Employers must ensure that blanking, blinding or double block-and-bleed systems are in place and can be used to isolate pipes containing harmful substances under pressure. Blanking involves inserting a physical barrier through the cross-section of a pipe so that materials are prevented from flowing past that point (see Figure 15.2) Blinding involves disconnecting a pipe and attaching a physical barrier to its end so that materials are prevented from flowing out of the pipe.

Figure 15.2   Example of blanking

Double blocking and bleeding involves use of a three-valve system where a pipe has two closed valves and an open drain valve positioned between them so that material is prevented from flowing and is re-directed in case of a valve leak (see Figure 15.3).  When used, a double block-and-bleed must be situated directly upstream of the work area. This means that if flow in the pipe can come from more than one direction, a double block-and-bleed setup is required on each upstream side. The valves of a double block-and-bleed system must be secured to ensure an acceptable level of safety. Securing must be by a “positive” mechanical means that is either

(1) lockable (operated by a key or similar device) and attached to or integral with the securing device, or
(2) not lockable but is strong enough to withstand inadvertent/unauthorized opening without the use of excessive force, unusual measures, or destructive techniques e.g. metal-cutting tools.

Figure 15.3  Examples of a double block and bleed

Piping that has been blanked or blinded must be clearly marked to indicate the presence of the blank or blind. Piping systems that contain harmful substances must be blanked, blinded or double block-and-bled before and during the repair, modification or replacement of the piping.

In some circumstances it may not be reasonably practicable to provide blanking, blinding or double block and bleed isolation. In these cases the employer must ensure that an alternate means of isolation is implemented. The alternative must

(1) adequately protect workers, and
(2) be certified as appropriate and safe by a professional engineer.