Improved portable circular power saw safety performance through riving knife design modification

Abstract

This study on portable circular power saw safety focused on body contact with an under-work protruding blade. Three guard were evaluated relative to injury severity, including two innovations and an unguarded saw with below-work configuration typically identical to one with a riving knife. Innovations consisted of riving knife modifications, including an ‘extended’ riving knife or ‘riving ring’, and a riving ring plus outrigger. Injury severity was simulated using human finger prostheses as test specimens.

Thirty single-specimen trials were conducted per experimental setup. For each trial the experimenter operated the saw, simulating a woodworking cut. An assistant fed specimens into the blade contact zone. After 90 trials, two medical raters ranked simulated severities using a five-level classification. Severities for riving ring plus outrigger proved significantly less than for a riving ring alone, which in turn caused significantly less severe injuries than a riving knife.

On the basis of severity level frequencies, it was concluded that the riving ring plus outrigger, which produced no injuries, represents the safest alternative tested. A riving ring without outrigger, which produced a significant number of minor injuries, represents minimally acceptable guarding.

The conventional riving knife, which generated significantly more finger-contact mutilation incidents than the other designs, was the most dangerous configuration. The research results do not detract from the significant benefits of riving knives relative to kickback prevention. However, both modified riving knife designs also possess identical kickback-prevention features.