This is Rob Siegel, the author.
The “double-jacking” I referred to was when using a floor jack–that I always jack a car up with the floor jack, set it down on the jack stands, then leave the floor jack in place. I was saying that the mid-rise essentially does that itself because, when the lift is set down on the stops, the hydraulic cylinders act like an in-place floor jack. I also said that, after the scare, I will, at times, when I am under the mid-rise lift for an extended period, put a wheel beneath it as an extra measure of safety. I am not setting the lift down on the wheel as a secondary method of support, nor am I advocating that anyone else set it down on a secondary method of support.
I completely agree that the lift needs to be in a fail-safe position at all times before working on the vehicle. It was, as I said, three things that conspired to have the lift depressurize while I was under it. One of those is the design of the latching mechanism of the lift itself. The latching mechanism on every mid-rise lift I’ve seen is not the same as the “dead man’s” design of the latching mechanism on a post lift, where the latches automatically engage when you raise the car.
I sincerely hope that no one has the same brain fart (not throwing the safety latch) and freakishly bad luck (kicking something that rolled into the down lever) I did. But alerting people that this CAN happen is one of the reasons I wrote the article.