Incidents involving hand fed or operated saws typically revolve around how the operator was holding or moving the workpiece through the saw. Common contributing factors include the operator placing an appendage too close to a blade, often with missing or malfunctioning guarding. Workpiece ejection matters usually relate to improperly secured workpieces. This may be the result of damage to the machine, missing components, or operator errors. Incidents on large commercial equipment with automatic feeding systems often involve a failure to properly deenergize the machine before working on it or a defeated guarding system.
Design, Guarding, and Features Most Often at Issue in Saw-Related Injury Cases
The removal of guarding or defeating of interlocks to allow operation with misplaced guarding is a common factor in machine accidents. Failure to de-energize machinery and lock it out before maintenance is also a common issue. When a work piece moves unexpectedly on a hand-fed tool, it can pull the operator’s hand into a rotating blade, causing lacerations or amputations. Cutting parts that are too small for the tool, loose knots in boards, and not using push blocks are common factors in these types of injuries. Entanglement or crushing by automated machines is usually due to missing or defeated guarding systems and failure to properly lock and tag out while servicing the machine. Workpiece kickback and ejection while making long straight cuts with rotary blades may be related to a missing riving knife. A riving knife is a fixed metal fin behind the blade that keeps the cut in the workpiece separated after it passes the blade. If the knife is missing, the cut can close against the back of the blade, pinching the blade and throwing the workpiece out of the saw. Dull or improper blade selection also contributes to kickbacks and unintended workpiece movement or ejection.
Critical Evidence to Preserve
Determining the most important evidence depends on what is in dispute. Typically, it is important to preserve the machine as it was at the time of the incident. However, it may not be an option to remove large pieces of commercial woodworking machinery from service for an indefinite period. If the machine must be returned to service, documenting the positions of all adjustments and settings should be done.
The workpiece and blades should also be preserved. The workpiece may contain tool marks that indicate the positioning and engagement of the blade during an incident. The position of the work piece should be documented if the scene is not preserved. Observing the type of blade and its condition is an important factor in determining the accuracy of the saw’s set up and maintenance. The availability and condition of alternative blade options should also be documented.
Failure Analysis and Standards
OSHA standards provide guidance on operator protection, guarding, and training that are expected in different environments, such as woodworking shops and sawmills. OSHA also addresses the expectations for control of free energy while servicing machines.
Consensus standards, such as the ASME B11 family of standards, ANSI 01.1, and UL 987, all provide additional requirements tailored for specific machine types. The consensus standards provide additional guidance on machine guarding, design, and expectations for employee training; often at higher level of specificity than OSHA.
Manufacturers’ instructions are specific to individual machines or a family of machines from a single manufacturer. They typically provide information on the intended use and operation of the machine, maintenance expectations, and selection of cutting tools. They also provide information on the intended configuration of the machine and available accessories for the machine. The parts diagrams and schematics available from manufacturers can be particularly useful when assessing why a machine is malfunctioning.
Evaluating Design and Proper Function
Many classes of machinery have specific design requirements for guarding beyond the general requirements in OSHA. When possible, the guarding requirements are determined prior to machine examination, and the available guarding is compared to the requirements during the examination. Interlock systems can be evaluated by machine operation or testing. They should be evaluated for functionality, ease of override, and potential tampering. When possible, security videos, incident reports, photographs, and other documents should be compared to the physical condition of the machine to provide an assessment of how the incident occurred.
Common modifications that contribute to injuries are removal or modification of a guarding system and defeating interlocks to allow machines to operate with guards missing or when improperly positioned.
Risk Management and Prevention
Creating a culture that understands, respects, maintains, and uses machinery as intended is critical from the designer to the end user. A tool that cuts wood or metal also has the capacity to cut flesh and bone. Even though well-designed, modern machinery now have systems to help mitigate risks, it is vital to follow appropriate procedures when working with these tools.
Most incidents involve a decision to do the job faster using a higher risk technique than recommended. This could be failing to properly deenergize machines when preforming maintenance or not changing blades to match the workpiece. Allowing machines to be operated without guarding, with damaged guarding, or with ineffectively modified guarding is another issue. These factors relate to issues in operator training and attitude.