Part II: Advanced Adjustment Mechanisms for Improved Ergonomics
By John-Paul McGovern, Ph.D., chief of research and technology, USSC Group, Inc.
This is the second installment in a series of articles discussing recent technological advancements in fire apparatus seat systems. This discussion will focus on advanced adjustment mechanisms for improved occupant safety and ergonomics. Future topics will be: advanced materials and coatings selection, integration, and optimization; advanced restraints integration and testing; and advancements in ride comfort and operator-fatigue reduction technology.
With USSC Group’s background in extreme-duty commercial and military seating systems; adjustment mechanisms such as fore-aft and recline; as well as mechanical, electrical, and air height adjust were straightforward features that would be standard offerings on the Valor line of fire truck and first responder seat systems. This question, however, was raised with industry experts: Are there additional adjustment mechanisms that could increase occupant comfort, safety, or egress speed?
The shortcoming that was identified was in the area of the bottle bracket positioning of a self-contained breathing apparatus (SCBA) seat system. Most current bottle brackets were adjustable in height by the bracket manufacturer, but currently fielded seat systems were only manually adjustable in the forward/rearward direction, and often required tools and a considerable amount of time to accomplish adjustments. Then, once adjustments were made to accommodate one occupant size, an occupant with a different body type would have to make such adjustments again—or simply deal with a nonideal SCBA bracket position.
While such a non-ideal position could surely be uncomfortable, it could also be unsafe in the case where seat belt position over the body is compromised and could also lead to impeded occupant ingress or egress. In the case where the bottle bracket is too far rearward for an occupant, the straps on the bracket would have to be adjusted longer than desirable simply to be worn in the seat. Then, when the occupant were to exit the truck with the pack attached, the straps would need to be readjusted for safe use in the firefighting/rescue situation.
With the need identified, USSC engineers set out to develop an automatically adjusting SCBA back panel such that an occupant is always positioned properly and comfortably in an SCBA seat. The driving requirement of such a design would be that the full occupant population should have their shoulders contacting the seat frame foam while in a seat with an SCBA tank present in the bracket and on the occupant’s shoulders. In this position, occupant protection would be optimized in all four instances of vehicle collision: forward, side-impact, rearward, and rollover.
To accomplish this, it was determined that four inches of forward/rearward adjustment would be required. In terms of mechanism type, it was determined that a four-bar swing link mechanism with locking ratchets between two of the pivot points would best serve the industry. Through this design, the required strength of the back panel for bottle retention in a forward crash event is maintained over the entire range of adjustment. This design would also allow the occupant to simply push rearward in the seat with his back until comfortable. The mechanism would then lock in this position, removing the weight of the SCBA bottle from the occupant’s back. If the occupant decided that he had pushed the bracket to far rearward, a pull handle on the side of the seat can be actuated to reset the mechanism to its farthest forward position.
Furthermore, the kinematics of the mechanism are such that for an occupant who requires the SCBA bottle to be more forward in the adjustment range, the bottle will also swing downward. This was a desirable attribute as it is generally shorter occupants who would require the bottle positioned more forward.
With extensive requirements compliance, strength, durability, lifecycle, and usability studies complete in 2013, the dynamic SCBA back design described above and shown in the images below was available in the fire/rescue market. User feedback has been excellent and applications with new manufacturers and new departments are accumulating rapidly.