A Practice in Restraint

At the request of a major US airline, the engineers at ThyssenKrupp Airport Systems Inc. set out to create a design that challenged conventional notions of PBB rooftop safety.

For maintenance personnel working atop passenger boarding bridges, the possibility of a fall has presented a safety risk. Systems have been devised to address the potential hazard — but not without concern for functional maintenance performance or effective injury prevention. Now a prototype, ThyssenKrupp believes the new system could prove a more effective solution.

A lack of effective safety measures
The majority of bridges currently in use are not furnished with any type of fall protection for technicians who must access equipment and features from a bridge rooftop. “The primary reason is that the bridges consist of two or three tunnel sections that telescope to provide the operational range of motion required,” says Clay Ratliff, director of customer service and after sales at ThyssenKrupp Airport Systems, a supplier of PBBs and various pieces of ancillary equipment. “Since the tunnels collapse inside each other and the clearance between tunnels is very small, it is difficult to provide a substantial structural anchorage point for traditional horizontal lifelines.”

Though a number of bridges are equipped with a handrail on top of the largest tunnel, workers are left without provisions on the smaller, retractable segments. An additional method has been to use tie-off points strategically located on each tunnel. Requiring a technician to unhook and reattach at various locations, it leaves a worker vulnerable between points. “So really there is no protection with strategic tie-off points for the worker when they are walking up and down the tunnel. It’s only when they are at that specific work location that they can attach,” Ratliff says.

A traditionally accepted solution for PBB rooftop safety has been a fall arrest system, which attempts to prevent injury or death in the event of a fall. It is designed to bring a user to an abrupt stop below the edge of the roof. A horizontal lifeline is placed on or close to the roof of each tunnel, the cables and support anchors typically within an inch of the roof for accommodation inside an overlapping tunnel, he says. A fall is arrested by a safety harness, safety lanyard and horizontal lifeline. However, several aspects of the system have raised concerns with experts in the industry.

A system flawed
“The biggest concern with this arrangement is that the person can still be severely injured in the fall,” Ratliff says. “The tunnels are steel or glass construction with a variety of attached devices that could cause injury to a person falling off the edge. The apron area around the bridges is also congested with numerous ground support vehicles and equipment that could be in the path of the fall.”

Another troublesome aspect has been that the bridge can be positioned at variable heights and is most often angled at a downward slope that might be close enough to allow contact with the ground or nearby equipment, according to Ratliff.

Additionally, Ratliff says, cables are pre-tensioned at the time of install. Under constant pressure, those cables can stretch over the years and increase the total fall length. “There is no uniform procedure to make sure those cables continue to hold that same amount of pre-tension,” he says.

OSHA has required systems to limit freefall to 6 feet. “In reviewing existing designs, it was determined that a fall could exceed the 6-foot threshold,” he says.

The fall arrest system has also presented an operational hindrance. “Due to anchorage point load requirements, this system is typically only rated for one technician to be on the roof at a time,” Ratliff says. At the end of each tunnel section, a technician must also disconnect and reattach to the adjacent tunnel.

In the summer of 2007, the team at ThyssenKrupp began the process of developing a system under a design principle that had been previously overlooked in the industry — preventing a fall from occurring, or fall restraint.

This content continues onto the next page...

We Recommend