Is that safe for working conditions if some pallet jacks won’t go down unless manually or there so rusted?

If you were injured at work, you may be entitled to Workers Compensation. That has become a bit of a speciality and you'd do well to find a lawyer who is well-versed in that area. You could try to find one online (for example, Avvo.com), or contact the Lawyer Referral Service at the State Bar, or check the yellow pages. As to whether or not the pallettes in their present state are unduly dangerous, a mere lawyer can have no idea without the opinion of an engineer or some other qualified expert. In addition to OSHA, many states have 'safe workplace' statutes and particular state agencies which enforce them. If you truly feel the pallettes are unreasonably dangerous, you could notify both the State and federal authorities. Consider the possible effect on your job though: bosses tend not to favour whistleblowers.