OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 5 Confined Spaces

Section 49 Protection – hazardous substances and energy

When a worker is in a confined space, uncontrolled energy sources and hazardous substances must be prevented from creating a hazard to workers. Examples of appropriate controls include blanking or blinding, double blocking and bleeding, misaligning or removing sections of lines, pipes or ducts, controlling all sources of hazardous energy, de-energizing equipment and immobilizing or disconnecting all mechanical linkages (see Figure 5.3).  In certain cases, alternate means of isolation and safe work procedures, certified by a professional engineer, may be used to protect workers.

Figure 5.3 Methods of controlling hazardous energy

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 5.4). Blinding involves disconnecting a pipe and attaching a physical barrier to its end so that materials are prevented from flowing out of the pipe. 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 5.5). The valves of a double block-and-bleed system need to be locked to ensure an acceptable level of safety.

Figure 5.4 Example of blanking

Figure 5.5 Example of a double bock and bleed

Special care must be taken to ensure that workers are protected against drowning, engulfment, entrapment or other hazards presented by free-flowing material(s) that may be encountered within a confined space. In some circumstances for example, a full body harness and lifeline system may be needed. See Table 5.2 for a list of common non-atmospheric hazards.

Table 5.2 Common non-atmospheric hazards

Common Non-Atmospheric Hazards


How it Occurs

Why You Should be Concerned

Engulfment Loose material drawn from the bottoms of storage bins can suffocate or bury an entrant. Liquids or materials are suddenly released into the space. Liquid or loose materials can trap or bury a worker in seconds.
Mechanical and Hydraulic Energy Mechanical and hydraulic equipment start or move unexpectedly. Entrants servicing mechanical and hydraulic equipment can be seriously injured or killed if the energy isn’t properly controlled.
Noise Confined space can amplify sounds produced by tools and equipment. Noise interferes with essential communication between entrants and attendants.
Falling Objects Objects fall into the space because topside openings are unguarded or improperly guarded.
Extreme Temperatures The space’s location and the equipment it contains make it very hot or cold. Hot environments put workers at risk for heat stress, especially if they are doing strenuous work or wearing protective clothing – cold environment make tasks more difficult to accomplish.
Slippery Surfaces Leaks, spills and condensation make walking surfaces slippery. Wet surfaces are usually slippery. They increase the risk of falls.
Corrosive Chemicals Corrosive chemicals are stored in the space, or entrants use them to do tasks. Corrosive chemicals can cause severe eye or skin irritation if exposed workers are not wearing protective clothing.
Access Problems Confined spaces are difficult to enter and exit. In an emergency, entrants may not be able to exit quickly.
Illumination Problems Most confined spaces are dark places. Poor lighting makes it difficult for workers to enter, exit and work in a confined space.