The required distance between a machine guard and a hazard depends primarily on the size and shape of the openings in the guard.

Under AS/NZS 4024.1801, guards must be positioned so that a person cannot reach through, over, under or around the guard and contact the danger zone. Larger openings generally require a greater separation distance because they allow more of the hand or arm to pass through.

For mesh machine guarding, the relevant factors include:

• the mesh aperture or opening size;
• whether the opening is square, rectangular or irregular;
• the distance from the inside face of the guard to the nearest hazard;
• whether a finger, hand or arm could reach the hazard; and
• whether access is possible from beneath, above or around the guard.

For example, a guard with a relatively small mesh opening may be positioned closer to the hazard than a guard with a large opening. A 50 mm square opening can permit significant arm access and may require a safety distance of approximately 850 mm, subject to the applicable table and risk assessment.

The distance should be measured from the closest accessible point of the guard opening to the closest point of the danger zone. It should not be measured only to the machine frame or the apparent centre of the hazard.

Safety distance is only one part of guard design. The assessment should also consider guard height, clearance beneath the guard, potential reach over the guard, foreseeable misuse and whether interlocked access is required.

The final design should be checked against the current edition of AS/NZS 4024.1801 and the machine-specific risk assessment rather than relying on a general rule of thumb.