I have personally never been involved with an OSHA audit; however, many of my clients have, and the stories they tell are often not very encouraging. It may not be as bad as an IRS audit, which I have been through, but they typically sound very close.
OHSA has stated that they will conduct an audit on a site for two primary reasons: one is a death or serious injury and two for a signed written complaint by a site employee. If an OSHA auditor shows up at your front door or lobby, they are required to let you know why they are there and will commence by talking to the senior person in the plant. You are allowed to keep them waiting for up to one hour, but after that, they will seek a court order to enter your property. Once you know why they are there, many OSHA auditors will want to first have you escort them to the area of concern for their personal inspection of that area.