Ergonomics of Traditional Leather Dying
by Walt Rostykus, CPE, CIE
The city of Fez, in northern Morocco, is the home of the world’s oldest leather tanning and dying operation. In the center of the medina (old city) is an area, about the size of a football field, filled with large vats built into the ground. This is where the task of tanning and dying goat and sheep hides has been performed for over nine centuries. Despite the stench, it is fascinating to view the leather workers processing leather the same way since the 11th century.
Being a safety professional, my first concern was exposure to the chemicals used in tanning and dying. These “natural” compounds include diluted pigeon droppings (acidic) for tanning followed by natural dyes (ex. henna, saffron, mint, etc.). This wet process means that workers are lifting, separating, and sorting wet hides while standing in each vat of “solution” (i.e. dermal contact). Each hide weighed around 25 to 70 pounds. This is where the ergonomist in me kicked in.
My Spidey Sense was tingling, letting me know that the manual handling of wet hides might exceed the limitations of what people can perform safely, increasing the chance of developing an MSD. Using an app for the NIOSH Lifting Equation, I determined that for lifting a wet and slippery hide, at arm’s length (20”), from the bottom of the vat to above shoulder (63”), the recommended weight limit (RWL) is 13.5 lbs. With the average weight of a hide being ~42 lb., the lifting index (LI) for this is 3.33. Based on our current knowledge of ergonomics and lifting, engineering or administrative controls should be implemented.
The irony of this situation is that for over nine centuries this task has been performed the same way, manually lifting one hide at a time. If I only had time to talk to the workers to learn what engineering or administrative controls they had tried, if any… In the pursuit of improving workplace ergonomics, sometimes it is best to enjoy traditional and cultural work practices for what they are—a tradition of craftsmen.
As tough a task as leather tanning is, the end result is a thing of beauty. Finished hides are transformed by craftsmen into leather goods, bags, clothing, and shoes.