I began with a chair configuration and ended with a hybrid of stretcher, cart and chair. The stretcher is a well-accepted first-aid tool, but not very practical for the narrow turnings and precarious gradients of fire stairs. Moreover, even if some adaptation of the ski patrol toboggan-type stretcher could be worked out, I could not image the typical ambulatory office worker test riding such a prone descent.
But there were two extraordinarily valuable ideas hidden in this stretcher application that set goals of performance for me. One, the evacuee’s weight should be carried directly by the stairs, not by human muscle. Two, the device should slide over at least two stair nosings at a time to provide a smooth passage over the stairs. Implied in this thought process was a very important, basic assumption. I was designing a universally usable, adaptable and completely portable evacuation unit requiring no installation. I also accepted evacuation of high-rise buildings as primarily a downward-directed activity.
Many see the EVAC+CHAIR® as an adaptation of the familiar tractor hand truck used to deliver refrigerators and other heavy appliances up or down stairs. It’s a comforting analogy and may have been a more logical point from which to start but it was in fact not self-evident at the start. The typical refrigerator hand truck is designed to go up as well as down. To do so with minimum effort, crawler belts run over roller bearings to reduce friction. These carts, built to transport heavy, bulk goods, are deigned to be handled one step at a time, using first the crawler and then the wheels on alternating stair nosing and tread. The realization of these limitations became extremely important as you shall see.