On Jan. 29, 2010, a 27-year-old machinist was fatally injured when he was struck by a piece of round stainless steel bar stock that he was machining in a computer numerical control (CNC) lathe. A coworker explained that the victim was machining washers for a gill net reel frame from the round bar stock. The machinist had placed a 6-foot piece of round bar stock into a Haas TL-3W model lathe. Approximately 3 feet of unsupported bar stock extended past the spindle.
As the victim monitored the lathe operation, the unsupported portion of the bar protruding through the spindle bent to an 80-degree angle.
The shop general manager speculated that the victim heard the noise generated by the rapidly rotating round bar stock and went to inspect. As the victim stepped to the back of the machine to inspect the source of the noise, the manager further surmised, he was struck by the bent piece of bar stock. The coworker and a contractor heard a crash sound in the vicinity of the lathe and, upon responding, found the victim unconscious.
What went wrong? The circumstances are simple to imagine, but there are series of errors in this situation that should be understood, and avoided.
- The 3-foot length of bar stock extending out past the spindle of lathe was unsupported.
- There was no system in place to support the length of bar stock extended past the spindle.
- There was no formal safety plan that addresses hazards regarding operation of lathe with bar stock extending beyond the spindle.
Also, CNC lathes’ ability to continue operating with unsupported bar stock extending past spindle is a problem that should be addressed in a general way. To prevent similar incidents from happening in the future the Washington State Fatality Assessment and Control Evaluation Team (FACE) recommends:
- Employers should ensure that machinery hazards are abated with engineering controls.
- Employers should develop and enforce machine and hazard specific safety policies and procedures that address and abate hazards.
- Employers should develop a mandatory checklist for each set-up procedure to ensure that all steps are properly completed before machines are started.
In addition, FACE recommends that CNC lathe manufacturers should design machines with multiple safety systems, including interlocks and “fail safes.”
Abate Hazards with Engineering Controls
To control hazards associated with a CNC lathes, or for other machines, FACE recommends that employers should follow the engineering hierarchy of controls. These controls, starting with the most effective, are:
- Eliminate or control hazard(s) by design.
- Control exposure to hazards by use of guards or safeguarding devices.
- Provide other safeguarding (e.g. awareness barrier).
- Implement administrative controls or other protective measures.
Following the incident described above, the employer manufactured a system to support bar stock that extends past the spindle. If this support system had been in place, the incident may have been prevented.
Employers that manufacture their own support system should work with engineers or companies who specialize in creating these support systems to ensure that the system is feasible and safe. Other methods to help abate this hazard include machine barriers to prevent workers from entering the path of a potential hazard; working with shorter lengths of stock; and cutting stock after material is delivered, so it will not extend past the spindle.
Another option, provided by the shop’s general manager, is to cover the spindle opening with a locking device. When an operator has a job that requires material to extend past the spindle, he must gain authorization from the safety manager to proceed, a system that’s similar to a lockout/tagout procedure. In order to get authorization to remove the lock, the operator would need to demonstrate that 1) it is necessary to have material extend past the spindle; and 2) the material will be properly and safely supported.
Manufactured support systems for extended bar stock are available from machine tool builders and specialized suppliers, such as J.F. Berns Co. Inc. These support systems can be manufactured with variable options and are available in a range of prices. Options include top loading functionality, retractability, and the ability to hold larger diameters of bar stock. (All Washington State employers are required to have in place a comprehensive Accident Prevention Program (APP) that is enforced and effective in practice. Samples of APPs are available from the state’s Department of Labor and Industries.)
Develop, Enforce Safety Policies and Procedures
Every employer should develop and enforce machine and hazard specific safety policies and procedures that address and abate hazards.
The employer in the case described here was aware of the hazards associated with having unsupported bar stock extending past the spindle, but there were no written safety policies or procedures to address or control the hazard until after the incident. The employer also reported that the victim had been corrected verbally on at least two occasions for setting up the Haas TL-3W lathe with bar stock extending past the spindle.
Safety policies and procedures are the basis of a safe workplace and should be created and documented before starting work on a new or existing job/task. The employer should perform or have a designated safety person perform a hazard analysis on all machine and task combinations. The hazard analysis should be used to identify and characterize the hazards as well as develop and document methods to control the hazards.
Safety plans should include enforcement policies, and should be updated before a new job or machine becomes part of the company’s work practices. Also, employers should review their safety plans periodically to ensure that they are controlling hazards effectively.
This employer’s safety plan would include policies regarding:
- The process for authorization to operate the lathe with bar stock extending past the spindle.
- What jobs are allowed to operate the lathe with bar stock extending past the spindle.
- How an operator must support and control bar stock extended past the spindle
- How to respond to an unexpected or hazardous condition.
- The consequences for violating these policies.
Develop Checklists for Every Set-Up
Employers should develop set-up procedures and ensure that each step is properly completed before any machine is started. Each product or production run set-up procedure should have a mandatory operator checklist that must be completed before starting a job.
A mandatory operator checklist would ensure that all system parameters, equipment settings, and safety precautions are properly made. In the case discussed here, completion of a mandatory checklist that included proper support for and length of material being machined could have resulted in the victim getting material from the short-stem rack, or cutting a longer piece of bar stock down to an appropriate length, thus preventing the fatality.
The last recommendation is more general than the others, and involves a commitment from the machining and manufacturing industry. Designers and contractors should design CNC lathes and machine installations with multiple safety systems, including interlocking safety systems and fail-safes.
The Haas CNC TL-3W lathe installed at the shop in the case discussed above had no safety system to prevent it from being operated with unsupported bar stock extending past the spindle. Interlocks ensure that machines cannot be operated until all safety devices are in place. Manufacturing this type of lathe with interlocks would have prohibited machine operation with unsupported bar stock extending past the spindle, and prevented this incident
A fail-safe device is intended to shutdown a machine if a hazardous condition occurs while in operation. Lathes should be designed and manufactured with fail-safes that will shutdown the machine if any material extending past the spindle becomes potentially unsafe. The ability to detect a hazardous condition, like material bending or becoming unstable, and to shut it down may have prevented this incident from happening.
About the author: Eric Jalonen, MPH, is a research investigator with the Washington State Fatality Assessment and Control Evaluation Program. Contact him at 360-902-6751, or by e-mail at [email protected]
The Washington State Fatality Assessment and Control Evaluation Program (FACE) developed this report. The FACE Program is supported in part by a grant from the National Institute for Occupational Safety and Health (NIOSH). For more information, contact the Safety and Health Assessment and Research for Prevention Program (SHARP) at 888-667-4277.