Isolating energy and clearing jams safely

Jam clearing and maintenance are where guards come off and where severe accidents are often located. HSE says lock-out procedures for interrupting mechanised production, such as freeing jammed timber, are "still a problem area". DGUV makes the same point from the design side by highlighting safety concepts for fault clearance and maintenance.

Stored energy: why "switched off" is not enough

A machine that has been stopped can still move. Energy can be stored as:

• gravity (a raised carriage, a suspended load, a stack of timber);
• hydraulic or pneumatic pressure (an accumulator, a cylinder);
• inertia (a coasting blade or flywheel).

Isolating a machine means cutting the supply and dealing with stored energy: releasing it, blocking it or otherwise making it harmless, and then verifying that the machine really cannot start or move.

Terminology differs by region

In the United States the OSHA standard 29 CFR 1910.147, "The Control of Hazardous Energy", is commonly called lockout/tagout. NIOSH states that employers must periodically inspect their written energy control procedures at least once annually under 29 CFR 1910.147(c)(6). That is a US rule.

In the EU the portal could not cite a single directive with the same title. The relevant pieces are the employer duties for work equipment (Directive 2009/104/EC), the Framework Directive's risk-assessment duty and the machinery design requirements. The text of the Machinery Directive's annex on energy isolation was not opened, so do not quote it. In practice, follow your national rules and the machine manual.

A skeleton isolation programme (the portal's interpretation)

1. For each machine, write a short isolation procedure: which isolators, in what order, how stored energy is released or blocked, and how isolation is verified.
2. Provide personal locks and tags and lockable isolators where people work, and group lockout for lines that several people enter.
3. Train and re-train, and have supervisors check that jam clearing is never done "just quickly" with the saw running.
4. Review procedures at least annually (as the US rule requires) and after any near miss.

Worked example: a jammed board at the trimmer

A board has jammed at a trimmer infeed. A tempting approach: reach in and pull it out while the line is paused. A safer sequence following the skeleton above:

1. Stop the line using the normal stop and inform the people working on the line.
2. Operate the isolator for the trimmer and apply your personal lock and tag.
3. Release or block stored energy: let the blade come to rest and secure any raised or pressurised parts according to the written procedure.
4. Verify isolation in the way your written procedure specifies, before anyone reaches in.
5. Clear the jam, using a tool where the procedure says so.
6. Refit guards, check that nobody is inside the danger zone, remove your own lock and restart.

If step 3 or 4 is unclear for a machine, that is a gap in the procedure, not permission to skip the step.

Group work and shift changes

When several people enter a line, the portal's article calls for group lockout so that the line is controlled for everyone inside it. The written procedure should also say how an unfinished job is handed over at shift change; the sources do not give a standard answer, so decide it in your risk assessment.

Design helps, but does not replace procedure

DGUV stresses designing machines so that protective devices are not tempting to bypass and that safe fault clearance is possible. If clearing a certain jam always needs a hand inside the machine, report it as a design problem; the risk assessment should deal with it.

Checklist: isolation audit

• Does every machine have a written isolation procedure?
• Are locks and tags available at the point of use?
• Is verification part of the procedure?
• Were procedures reviewed in the last twelve months and after the last near miss?
• Do supervisors observe jam clearing in practice?

Key points

• Jam clearing and maintenance are a recognised problem area in sawmills (HSE, DGUV).
• Stored energy (gravity, hydraulic, pneumatic, inertia) must be released or blocked, and isolation verified.
• The annual-review rule quoted is the US NIOSH/OSHA rule; the EU has no single equivalent text cited in the portal.
• Use personal locks and group lockout; never clear a jam "just quickly" with the saw running.
• Review procedures at least yearly and after near misses.