For a quick 'back story' on my comments, I have 3 steel pins in my left arm from a car falling off a jack stand and jack while I was under the car. I was on gravel (mistake) and changing the clutch in a 1970 Camaro when I noticed that both the jack and jack stand looked like they were moving. A few seconds later it dawned on me, as I was staring at them, that the car was going to fall on me. I rolled as fast as I could out from under the car but ended up getting my left arm, just below the elbow, smashed under the rocker panel. Since I was by myself, it took me almost a full hour to dig the gravel out from around my smashed arm with my other hand to finally free myself. It seemed like it took forever to drive myself to the hospital too. As I'm sure you can imagine, that incident isn't something easily forgotten.
That is why I always, and I mean always use jack stands if I'm under a car now. Actually, I have 3 lifts between my barns, so I rarely crawl or roll on a creeper under a vehicle anyway. If I do, you can bet your life that I have at least 2 jack stands under the vehicle and it won't be on gravel. I won't trust a HF floor jack at it's max rating, but it wouldn't bother me at all to use 2 HF 3 ton jack stands under the front of an average vehicle. For that matter, it wouldn't bother me at all to even use a HF floor jack to jack up the vehicle. I just wouldn't trust my life on that jack not failing in any way. Now, with my back story, I think you can understand why I'm so adamant about that. I got away with being stupid once. I don't ever plan on testing my luck that way again in this lifetime. Make more sense?