By Design: A little mistake with fatal consequences

A story of how failure to add UV absorber when switching from dry to liquid colorant may have been a critical error.

This story is based on an actual event. Some of the details have been changed to protect those who were involved.

There was some wind, but the sun was shining and it was the first warm Saturday of the year. A father and his 7-year-old son seized this opportunity to go fishing. They loaded their 14-foot, flat-bottomed, aluminum boat with the usual fisherman’s gear, including life preservers. Of special interest was an injection-molded fisherman’s chair, clamped to the boat’s horizontal bench seat. The chair as purchased was equipped with a swivel, which allowed the user to rotate 360º for freedom in fishing and to attend to the boat’s outboard motor.

The father and son were observed wearing their flotation vests while fishing in a sheltered cove. Later that day, a second shore-based witness testified that the father was not wearing a flotation vest as the boat made its way out of the cove and into the main body of the lake. The witness stated that as the boat left the cove, it encountered rougher water and began to rock. He said that the front of the boat rose up high enough for him to see the -inside bottom deck, and the father was observed falling backwards and tumbling out of the boat. The boat continued traveling in a large circular path. Evidently, the son didn’t know how to handle the boat or was too shocked to do so.

The father swam toward shore while the witness and his party rushed to launch their own boat. For some unexplained reason, the father stopped swimming and disappeared from sight. The rescue boat circled the area but could not find the father. They picked up the son who had jumped from the boat while still wearing his flotation vest. The father’s body was recovered. The coroner’s finding was accidental death by drowning.

The boat was retrieved. The chair was found to be broken. As can be seen in the photograph, the brittle fracture was just behind the area where a metal plate attached the swivel to the chair. The deceased’s family filed a suit claiming design and manufacturing defects. The suit named the discount retailer who put the chair into the stream of commerce and the proprietary injection molder who produced the product and sold it to the retailer.

Finding fault

The chair was molded using premium-grade polypropylene (PP). This was a logical choice, as PP has a long and successful history of use in both consumer and commercial seating. However, in this case something went terribly wrong.

It only took a glance to realize that the accident chair had been severely attacked by exposure to ultraviolet (UV) light. Referring to the photograph, some of the original green color can be seen on the bottom of the chair, which was not exposed to direct sunlight. The color is the strongest in the area shielded by the metal swivel mounting plate. Both sides of the back, and especially the top of the seat, have lost most of their color. The chair was so degraded that it was possible to scratch some material off of these surfaces with a fingernail.

All materials are affected by outdoor weathering. Some metals oxidize, others rust; wood bleaches, dries out, and shrinks; the pigments in paint and plastic fade. All of these materials are affected in different ways and degrees. Some plastics, such as polyvinyl chloride and acrylic, are very resistant to outdoor weathering. Others are attacked by UV light. In some cases, the attack is severe enough to result in a loss of the material’s physical properties.

The useful life of PP in outdoor applications can be extended by incorporating a UV absorber in the material. A document search indicated that the molder had been purchasing a UV absorber mixed with a colorant from a well-known pigment supplier.

As far as is known, the chair experienced approximately two years of outdoor exposure. The chair exhibited more UV degradation than what would be expected. This raised the question as to whether or not the correct type or amount of UV absorber had been used. The three round holes shown in the chair’s photograph were hole-saw cutouts for testing. Infrared analysis indicated that there was no trace of the UV absorber on the surfaces of the chair directly exposed to the sun or on the protected bottom surface of the seat.

Ultraviolet absorbers are consumed in performing their intended function. It is, however, unlikely that two years of exposure would have used up all of the UV absorber through the whole thickness of the part or on the bottom of the seat. The conclusion that must be drawn is that there was no UV absorber in the material used to mold the accident chair.

As near as can be ascertained, the molder tumble-blended PP with the dry powdered pigment and UV absorbers. After some years of successful production, the molder changed from a dry powder pigment to a liquid coloring system. There is a high probability that the molder, or the pigment supplier, made a mistake in not including the UV absorber in the change from dry to liquid colorant.

Lessons learned

At the time of this accident, there were no performance standards for marine seating. Chairs were tested using the ANSI office chair standards. The chairs passed this test, but these were recently molded parts with no outdoor exposure. The molder’s original written purchase orders specified a blend of pigment and UV absorber. This indicated that they knew that the PP needed protection from UV light. The lack of a UV absorber in the accident chair and on the liquid color purchase orders was a simple mistake with dire consequences.

These circumstances made it difficult to argue this case in court. There was little or no chance of prevailing before a jury with two small children and a young, grieving widow sitting in the front row of the courtroom. The defendants filed for a summary judgment. The retailer’s attorney argued that it was not the chair, but the boat rocking-wave action and the father’s failure to wear a flotation vest that caused the accident. The molder’s attorney claimed a lack of responsibility as the chair was beyond its one-year warranty.

Summary judgment was denied, and the case was settled out of court for an undisclosed amount with no admission of responsibility. A father is dead. A son has nightmares. A family is irrevocably changed. We are on our own in deciding who is culpable.

Today, companies change from one supplier to another to save pennies. Many of those purchasing decisions are made by non-technical people who wouldn’t appreciate the importance of a UV absorber.

The moral of this story is to be careful. Small mistakes can have fatal consequences.