Barrier guarding is the most common method of machine safeguarding. Preventing machine-related injury continues to be a priority at the National Institute for Occupational Safety and Health (NIOSH) and for safety professionals in industries as diverse as manufacturing, agriculture, and mining. Between 1996 and 1998, there were 464 occupational fatalities (an average of 155 per year) reported to the U.S. Department of Labor's Bureau of Labor Statistics as specifically involving caught-in running machinery. The majority of these were agricultural-machine-related. For the 1995–97 period, there were 92,932 cases of nonfatal injury of this type involving lost workdays. The majority of these (65%) were in the manufacturing industry.

Determining which guard can best prevent a machine-related injury presents a significant challenge to safety engineers. A major part of the challenge is that the risk of injury involving machinery varies greatly from task to task. When the level of risk for a task has been correctly assessed and reduced, a guard that is effective, at that risk level, will have been designed, installed and used to control the risk. This presentation will help safety engineers to work with other engineers to select and design effective barrier guards.

The following terms will be used in the problems presented: (available in full paper)


Barrier guarding is the most common method of machine safeguarding. Safety engineers frequently team up with other engineers and operating personnel to put protective barriers in place. To function effectively in such a team, safety engineers need an understanding of analysis tools used by other engineers (Clemens, 1999). They also need to appreciate the human factors involved in how guards are used. Machinery safeguarding selection is characterized by the options in the devices and methods that might appear to be equally applicable for the same task.

This paper provides a brief overview of the types of analysis that have to be performed when designing or selecting guarding. This presentation will empower you to work with other engineers and operating personnel to select and design effective barrier guards. This article will describe the various reliabilities of mechanical safeguard design and how they relate to selecting safeguards based on risk to the operator. Technical guidance about the levels of reliability for designs within mechanical safeguard types should be useful for users of U.S. machine guarding standards.

Injury Risk is examined with respect to the severity and degree of exposure for potential injuries. Strength of materials is first reviewed from the perspective of the strength of bio-materials and the thresholds above which they cannot absorb mechanical energy without fracture. Risk Reduction is then addressed in the design of protective structures that can safely absorb mechanical energy. Design considerations are discussed that are appropriate when bending forces could move the protection aside or when dynamic penetration forces could allow a high speed object to pass through a barrier. Systematic Risk Assessment is then covered, going into the selection of risk reduction measures that are reliable enough, by their design, installation, and expected use, for the severity and exposure potentials of the task.

This content is only available via PDF.
You can access this article if you purchase or spend a download.