When a concrete boom collapsed on the job, the contractor was irked at the inconvenience, but grateful no one had been hurt. When the second boom collapsed, he figured it was terrible luck. But when the third boom collapsed, he called me to do an accident investigation.
Last month (“Outside the plant, safety lapses burn the public, too,” Jan. 22, 2009) I wrote about hazards that occur when work must be done outside an enclosed shop. I remarked that manufacturers of rolling stock, equipment that is driven or towed to an external work site, have made great strides in protecting both users and bystanders.
Manufacturers of concrete pumps and booms, which deliver concrete slurry to parts of the work site the mixing truck can’t reach, are no different. In the case of the concrete booms I investigated, the abrasive sludge wore the tubing walls away, weakening them. To alert users to the wear, the boom manufacturer indented the tubing wall. When the concrete started to leak through worn indents, it was time to replace the tubing.
My investigation showed the walls of the collapsed tubing were too thin to support the load even before the indents wore through. The boom manufacturers have since found a better way to monitor tubing wall thickness.
There were no injuries in the concrete-boom case, but many of those who work with concrete pumps have not been so lucky. The area around the hopper, where the ready-mix truck dumps the concrete into the pump, is one of the most accident-prone.
A grate guards the valve area of the pump. But during cleanup operators frequently remove the grate for easier access to the pump and valve, sometimes while the system is running. This dangerous practice has cost many workers their fingers, hands, and even their lives.
OSHA’s Lockout/Tagout requirement directly addresses this issue, but it is reasonably foreseeable that workers ignore LO/TO. In 1995, the industry created the Concrete Pump Manufacturers Association (CPMA), led by manufacturers Putzmeister and Schwing America, to examine this problem. They first adopted a version of EN 12001, the European standard for concrete pump safety, which had been in place in Europe for many years. In 1997, Reed and other concrete pump manufacturers joined to create CPMA Standard 27-2000, first issued in October 1999.
The focused effort continued until a revised version published by ASME/ANSI in 2006 as ASME B30.27 gave the rules third-party heft and visibility. Among other things, this standard incorporates the use of interlock systems that shut down the pump if the grate is not in place, an approach some manufacturers have used since 1999.
This Putzmeister-designed switch shuts off the concrete pump when the safety grate is raised.
My thanks to Jim Burg of Putzmeister and Robert Edwards, formerly of Schwing America, for their assistance with this week's column.
Lanny Berke is a registered professional engineer and Certified Safety Professional involved in forensic engineering since 1972. Got a question about safety? You can reach Lanny at [email protected].