There is arguable ambiguity in the structure, but the meaning of the various parts resolves it.
Who may be exposed to is the lead into a list, which ends at may cause injuries. The question is whether that may cause industries applies to the whole list preceding it, or only the last part - is it applying to the list, or is it part of one item in the list? Now, any reasonable manual of style or rigorous analysis will tell you that it's part of the last part of the list. That's because the or cannot be indicating that penetrating actions is the last item in the list, because "being exposed to crushing" would be far less likely than "being exposed to crushing actions", especially given the existence of "penetrating actions". Some will argue that it's the commas that tell you this, but commas are rarely a totally reliable indication. Many manuals of style will find it perfectly acceptable to say "I want to thank my parents, the Pope and Nelson Mandela", and that is syntactically ambiguous (and thus a source of humour).
So, we now have a list of things employees may be exposed to foot injuries1 from:
- hot surfaces
- corrosive materials
- crushing or penetrating actions which may cause injuries
(Plus, the wet locations thing which isn't related to foot injuries - but that would certainly lead to a need for good footwear.)
Whether the "foot injuries" is part of the introduction to the list, or part of the first item, the fact that it exists suggests that the "may cause injuries" would lead to redundancy if it applied to the whole list, which is another point in favour of it being part of a single item on the list. If the "foot injuries" is part of the first item, then it's just that only the first and last items are referring to injuries. That would be odd, but not beyond the pale. If "foot injuries" is part of the introduction to the list, the "may cause injuries" is an acknowledgement that not all crushing or penetrating actions will cause injuries.
1: or "foot injuries" is part of the first item in the list. That's ambiguous as well, but context might make it clearer - if the PPE in question is just footwear, than it's a list of sources of foot injury; if not, it may well not be.