What are my rights if an on-site vendor supplied a faulty respirator given to me at work and I have been overexposed as a result?

Since you were injured at work, you would have a worker's compensation claim which would compensate you for your injury including your medical bills and pain and suffering.  Your employer's human resources department should have the documents you will need to file your worker's compensation claim.

Your worker's compensation claim is separate from your claim against the third party vendor, who supplied the faulty respirator.  You can sue the vendor for negligence.  Negligence is the failure to exercise due care (that degree of care that a reasonable vendor would have exercised under the same or similar circumstances to prevent foreseeable harm).  In other words, if a reasonable vendor would have performed a hazard assessment to be certain it issued the proper respirator and cartridges, and the third party vendor in your case did not, you can establish that your vendor was negligent.  In order to prove negligence, you must prove duty of care, breach of duty, actual cause, proximate cause, and damages.  The failure to perform a hazard assessment for issuing the proper respirator and cartridges breached the duty of due care.  But for the failure to perform the hazard assessment, would you have been injured?  If the answer is no which appears to be the case, you have established actual cause.   Proximate cause means are there any unforeseeable intervening acts which caused your injury?  If the answer is no, the vendor is liable for negligence and you have established the elements to prove negligence.  You also need to prove damages (amount of monetary compensation you are seeking) which in this case would be your medical bills, medical reports to document the nature and extent of your injury and if applicable, compensation for wage loss.

 Compensation for the medical bills is straight reimbursement.  The medical reports as mentioned document the nature and extent of your injury and will be used to determine compensation for pain and suffering, which is an amount in addition to the medical bills.  Compensation for wage loss is straight reimbursement.

Prior to filing a lawsuit against the vendor, it may be possible to settle the case with the vendor's insurance carrier.  Your claim filed with the vendor's insurance company should include your medical bills, medical reports and documentation of wage loss.  If the case is settled with the vendor's insurance carrier, NO lawsuit is filed against the vendor.  If you are dissatisfied with settlement offers from the vendor's insurance carrier, reject the settlement offers and file a lawsuit for negligence against the vendor.  If the case is NOT settled with the vendor's insurance carrier, your lawsuit for negligence against the vendor must be filed prior to the expiration of the applicable statute of limitations or you will lose your rights forever in the matter.

The main issue is: have you in fact been harmed (e.g. sickened or made ill in some way)? The law does not provide compensation for being exposed to threats or risk, or for what could or might happen; it only provides compensation for actual injuries and costs (such as medical costs). Even if you were overexposed, if nothing happened due to that exposure, you would not have a viable legal claim and would not be entitled to compensation.

If you were injured in some way, then to prove what the vendor should have done, you'll need an expert witness, such as a safety consultant, who can testify as to what the vendor is required to do and/or as to what would be reasonable and standard safety precautions.