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A newsletter dedicated to keeping attorneys informed of the technical side of product liability cases.
Issue 66: January/February 2017
Gurading by Distance
By John L. Ryan, P.E.
© 2017 M.A.S.E. LLC
Guarding by distance protects people from hazards by providing adequate distance to the hazard, while considering accessibility factors such as how close a person can get to the hazard due to partial barriers or holes in guards for accessing machine parts or the point of operation.
Guarding Point of Operation by Distance and Sensing Device
Guarding by distance is used in the case of machines such as power presses where the operator needs access to the point of operation in order to place and retrieve the part. A sensing device detects when a person may be nearing the hazard zone. The sensing device could be a light curtain, a body bar, a presence sensing mat, a limit switch, or other device. The primary concern here is that the person cannot reach the hazardous point before the machine has come to a stop or safe position.
The two primary variables at work here are the speed that a person moves and how long it takes a machine to stop. OSHA provides simple calculations to determine what the safety distance between the sensing device and the hazard point is. This method is an acceptable method of ensuring that a machine operator cannot reach a hazardous part of the machine before it comes to rest. Machines that have linear motion will tend to stop much more quickly than machines with rotational motion, unless that rotational motion element has a braking device. Various standards require machine motion to come to a complete stop before any person has a chance to be exposed to the hazard.
Guarding Point of Operation with Barrier Guard and Distance
Some machines rely on a combination of a barrier guard and distance to provide adequate hazard protection. Machines that would use this type of guarding configuration include any type of machinery that involves linear movement of product, whether food, steel, plastic, or other material. This concept also becomes applicable whenever a hazard point is unguarded, and potentially accessible by someone.
Using a Safe Distance Based on Accessibility Parameters
Various standards identify the required distance to unguarded hazards based on the opening allowing access to the hazard. These standards include 29 CFR 1910.217 Mechanical Power Presses, ANSI B11.19 Performance Criteria for Safeguarding , Vaillancourt and Stover’s A Review of Machine Guarding Recommendations, ASME B15.1 Safety Standard for Mechanical Power Transmission Apparatus, ISO 13852 Safety of Machinery – Safety Distances to Prevent Danger Zones Being Reached by the Upper Limbs, as well as other standards and references. An opening in a barrier guard that facilitates product loading and unloading is also subject to these requirements. Some standards utilize risk assessment to determine risk severity to determine required distances to hazards. The following charts summarize the requirements of gap and distance to hazard:
The size of an opening in a guard dictates the allowable distance to a hazard
Guarding Overhead Hazards by Distance
Overhead hazards have historically commonly been guarded by distance. This seems like a simple concept - as long as there is adequate clearance above people, then there shouldn’t be any contact with the hazard. Unfortunately, these standards assume an individual is on his feet, and don’t take into account step stools, ladders, work platforms, tools, and helmets. The standards that govern guarding overhead hazards by distance are minimum standards, and individuals in the top percentile in terms of height would likely still be able to make contact with these overhead hazards. Other considerations include whether maintenance activities will expose individuals to these hazards that are only guarded by vertical and horizontal distance.
How We Can Help
At MASE, we have expertise in determining if an industrial accident was caused by an improperly guarded machine, and developing alternate designs to make the machine safe. Don’t go it alone—opposing counsel will likely have an engineering expert whose testimony will have to be mitigated. Call us at (855) 627-6273 or email us at email@example.com
Any machine guarding related industrial accident should be reviewed by a professional engineer in
order to determine accident causation and to see if any standards were violated in the design,
production, or use of the machine.
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© 2017 Mechanical and Safety Engineering