The self-insured employer appeals the compensation judge’s finding that the employee’s December 18, 2006, injury did not result from the employee’s performance of a prohibited act.  We affirm.

Donovan Michaels, the employee, sustained a severe laceration to his right arm while working for ADM Milling Company, the employer, on December 18, 2006.  The self-insured employer initially admitted liability for a personal injury and commenced payment of workers’ compensation benefits.  Thereafter, the employer sought to discontinue workers’ compensation benefits contending the injury arose out of the employee’s performance of a prohibited act.

The employee began working for the employer in 1995 as a car cleaner.  He received several promotions and on December 18, 2006, was working as a grinder in the Mill Department of the employer’s Nokomis plant.  The injury took place on Monday morning while the employee was cleaning a running drive belt on a wheat grinding machine.  Wearing gloves and with a Scotch Brite pad in each hand, the employee reached over a guard on the machine and with each hand placed a pad on the upper and lower sides of the moving belt.  While doing so, the belt caught the employee’s glove, pulled him down, and lacerated the upper part of his right arm.

At some point, certain machines in the plant were driven by belts made of leather.  When leather belts were used, the belts needed to be cleaned or scuffed up to prevent slipping.  The leather belts were replaced and the belts in use on the date of the employee’s injury were rubber backed.  The employer contends the rubber backed belts did not need to be cleaned and asserts the employees were instructed not to clean the belts.  The employer further contends all employees were specifically prohibited from working on any machinery before de-energizing the machine and then following a “lockout/tagout” procedure.  The self-insured employer contends the employee specifically violated both prohibited acts.

There was extensive testimony at the hearing involving safety procedures and belt cleaning.  Patrick O’Hara was the Safety and Sanitation Director for the employer at its Nokomis plant.  In 2002, Mr. O’Hara conducted a behavioral safety training program, which was held off the employer’s premises.  The training program was designed to focus on unsafe acts by employees rather than on unsafe equipment.  At this program, the employees were told that before working on, cleaning, or repairing a machine, the machine must be de-energized and a “lockout/tagout” procedure followed.  To de-energize a machine meant that all power sources to the machine must be turned off.  “Lockout/tagout” meant a lock was to be placed on the energy source for the machine and a tag was to be placed on the machine to prevent other employees from restarting the machine.  Mr. O’Hara documented the “lockout/tagout”procedure was discussed at monthly mandatory safety meetings at least once a year, and the employee was present at these meetings.  He stated the machine upon which the employee was working when he was injured was powered by an electric motor and was covered by the lockout/tagout procedure.  Mr. O’Hara testified the employees were also specifically instructed never to remove or reach around guards while equipment was operating.  Mr. O’Hara stated that the drive belts were not to be cleaned.  Mr. O’Hara testified he observed Monday morning startups many times over the prior five years and never observed anyone cleaning the drive belts.

Jeffrey Skiba, the plant manager since 1992, was responsible for product quality, managing the work force, and safety procedures, and he was the employee’s direct supervisor.  Mr. Skiba testified the employee was advised of the “lockout/tagout” procedure.  Mr. Skiba acknowledged the Nokomis plant in the past had used leather drive belts, but testified the belts on the machine in 2006 did not need to be cleaned.  Further, he testified if any work was to be done on any machinery, the machine needed to be de-energized and the “lockout/tagout” procedure followed.  Mr. Skiba testified he never saw employees doing belt cleaning.

Charles Hatch became the general plant manager at the Nokomis plant in 2001.  He testified all employees were specifically prohibited from reaching into or working on equipment which was not de-energized and locked and tagged out.  Mr. Hatch further testified that since the safety training in 2002, he personally had not seen any employees cleaning belts.

The employee testified he attended the safety meeting in 2002 and understood that when he worked on a machine, he was to de-energize the machine and then lock it and tag it out.  The employee further acknowledged attending safety meetings in September 2003, August 2005, and June 2006 where the same topics were discussed.  However, the employee stated that after the plant was cleaned over the weekend, debris such as flour and farina collected on the belts and they needed to be cleaned every Monday morning.  He denied ever having been instructed not to clean belts.  Rather, the employee maintained cleaning the belts was a part of the normal Monday morning startup process which he was taught to do every Monday.  Further the employee testified he was instructed to clean the belt by the bolter who was his immediate supervisor.  The employee stated if he didn’t clean the belt there was a strong possibility the belt would come off.  He testified belt cleaning was performed “religiously” every Monday morning.  It was not possible, the employee stated, to clean the belts with the machine turned off.  The employee stated he used Scotch Brite pads to clean the belts.  The pads were kept in a closet in Mr. Skiba’s office, and the employee testified he had a key to the office so that he could obtain the pads he needed each Monday morning.  The belt the employee was cleaning was approximately 36 feet long and it took only a few seconds to clean the moving belt.

Douglas Peltier worked as a grinder at the Nokomis plant for over 20 years prior to his retirement.  He testified cleaning the drive belts on Monday morning was a routine procedure which he was taught to do when he became a grinder.  Further, Mr. Peltier testified the bolters that he worked with insisted that he perform the cleaning every Monday.  Prior to the employee’s injury, Mr. Peltier denied ever being instructed not to clean the belts.  Despite the safety meetings and the lockout/tagout procedures, Mr. Peltier stated the bolters he worked with continued to instruct him to clean the drive belts.  Following the employee’s injury, an announcement was placed on a bulletin board instructing the grinders to stop cleaning the belts.  Thereafter, Mr. Peltier testified belt cleaning was no longer performed.

Following a hearing, the compensation judge concluded the belt cleaning process performed by the employee on December 18, 2006, was routine, expected, and a necessary part of the employee’s position.  The compensation judge further concluded the employee did not perform a prohibited act and found his personal injury arose out of his employment.  The employer appeals.

The prohibited act doctrine is a common law exception to the general rule that an employee’s misconduct is not a defense to a claim for workers’ compensation benefits.  In Bartley v. C-H Riding Stables, Inc., 296 Minn. 115, 120, 206 N.W.2d 660, 663, 26 W.C.D. 675 (1973), the Supreme Court held that where

The appellant asserts it established the drive belts were not to be cleaned, the employee knew of the prohibition, the prohibition was customarily observed, the employer took reasonable steps to the enforce the prohibition, and the performance of the prohibited act was unreasonably dangerous.  The appellant contends the compensation judge erred in concluding the prohibited act doctrine did not apply.  Accordingly, the appellant asks this court to reverse the compensation judge’ decision.  We decline to do so.

Where evidence is conflicting or more than one inference may be reasonably drawn from the evidence, the findings of the compensation judge are to be upheld.  Redgate v. Sroga’s Standard Serv., 421 N.W.2d 729, 734, 40 W.C.D. 948, 957 (Minn. 1988).  In this case, the employee and Mr. Peltier testified belt cleaning was a routine part of the Monday morning start up which they were instructed to perform.  Both testified the belt cleaning process was not specifically prohibited and both denied they were ever told belt cleaning could only be performed when the machines were in the logout/tag out status.  The compensation judge accepted the testimony of the employee and Mr. Peltier which the judge found credible.  The assessment of witnesses’ credibilty is the unique fiunction of the trier of fact.   Tolzmann v. McCombs Knutson Assocs., 447 N.W.2d 196, 42 W.C.D. 421 (Minn. 1989).  The judge concluded the self-insured employer failed to establish the employee knew of the prohibition against belt cleaning or that the prohibition was customarily observed.  As the decision of the compensation judge is supported by substantial evidence, it must be affirmed.  Hengemuhle v. Long Prairie Jaycees, 358 N.W.2d 54, 37 W.C.D. 235 (Minn. 1984).