Collapse into the ravine, less so falling into it where hands would attempt to break their fall and produce wrist/collar bone injury, could explain the flail chest. Perhaps significantly Semyon was found laid on his flailed right side, and quite possibly Lyuda was the same before her body effected a dam against the increasing flow of meltwater and was washed over the rock, her post-rigor mortis joints assuming a new kneeling position.
Resuscitation could also explain some rib fractures too. I read a study which showed that in 71% of cadavers presenting at autopsy after CPR there were multiple rib fractures and the ones affected were broadly the same as in the DPI, although the DPI fractures should be slightly to the left of the sternumif from resus, not over to the right as with Lyuda and Semyon.
Some of the injuries, the burns to Krivo's leg particularly, and Doro's scalp could apply to nitric acid exposure, but I don't recall the pathologist noting any yellowness of skin, and he was describing the colour of everything, skin, eyes, meninges, urine, ear auricles. From memory I recall that two hikers were described as having a bluey tinge to their skin, such as bluey-red or bluey-pink, which made me wonder if they had developed cyanosis from low blood oxygen (keying in with Solter's claims of suffocation), so they certainly weren't all yellow.
Igor Dyatlov, on the slab, looked like you could snap your fingers and he would wake up and tell you what happened, he didn't look burnt, or even frostbitten, although the body of his report claimed he had frostbite to his "extremities", so if chemical burns were sustained they were specific to some of the hikers, not all of them. To run with that maybe they were in different places when it happened, such as 4 of the at the forest collecting wood and they got the worst of it and tried to shelter inside the ravine.
I'd suspect that if evergreen trees had been exposed to an acid mist, then like acid rain more than just the growing point would be affected. Evergreens being wider on the lower branches, the opposite habit of the crown of a deciduous, so right down the evergreen tree the foliage would be burnt, or browned.
If the hikers were affected by a mist then unless some of them were in a different place when this happened, such as collecting wood, they should all be affected, and have a yellow tint to their skin, the mucous membranes of their eyes would be affected, and the lungs and the inside of the nose, and the mouth when mouth breathing, and the throat. But the pathologist didn't seem to make any of these observations.
If faced with an acid mist wouldn't the hikers be more inclined to cover up rather than remove clothing and footwear, and perhaps attempt to shorud themselves with their blankets, which would then become useful for survival elsewhere.