Part I: Modeling, Simulation, and Testing
By John-Paul McGovern, Ph.D., chief of research and technology, USSC Group, Inc.
This is the first installment in a series of articles discussing recent technological advancements in fire apparatus seating systems. This discussion will focus on computer-aided modeling, simulation and testing of the newest and most innovative seating systems available in the market today. Future topics will be: advanced materials and coatings selection, integration, and optimization; advanced adjustment mechanisms for improved ergonomics; advanced restraints integration and testing; and advancements in ride comfort and operator-fatigue reduction technology.
In setting out to bring a new line of fire apparatus seating systems to market, engineers at USSC have drawn on an extensive company background of extreme duty seat design and testing in commercial, rail, and military markets. Federal Motor Vehicle Safety Standards (FMVSS) compliance analysis, simulation, and testing were commonplace tasks for USSC designers, but the corporate initiative to enter the fire apparatus market required application of these test principals to new and diverse seating systems. Specifically, the need for self-contained breathing apparatus (SCBA) accommodation in fire apparatus seating required seat back frame structures that were entirely open in the central area but still of sufficient mechanical strength to comply with FMVSS regulations. These regulations are of particular importance in all belts to seat (ABTS) applications where all occupant restraint loads must pass through the seat system to the vehicle structure.
To accomplish this design task, engineers first used computer-aided design (CAD) and finite element analysis (FEA) to iterate the design of the base plate mounting structure, the SCBA back frame and the interface of the two. Photo 1 shows the CAD design at left in its meshed state.
Photo 2 shows the FEA test setup for FMVSS simulation. By performing the design and simulation in this way, critical elements of the design like tubing wall thickness, hardware size and location, as well as restraint harness placement and mounting configuration were able to be iterated rapidly and accurately to provide for an optimized system and expectations of a successful physical certification test.
Photo 3 shows the physical test performed in USSC’s engineering test lab for final physical validation of the final seat design. As predicted by the FEA analysis performed, the physical test confirmed that the prescribed loads of 3,000 pounds to the torso block, 3,000 pounds to the lap block, and 20 times the weight of the seat applied at the horizontal plane of the center of gravity were all reached within 30 seconds and sustained for 10 seconds. A subsequent test showed that the ultimate strength of the seating system actually far surpassed these required load values.
By virtue of this and other certification testing, the Valor line of fire apparatus seating was demonstrated to exceed industry safety standards and provide an extreme duty product that also possesses industry leading comfort and ergonomics.