Well yeah clearly we document and inform customers of potential problems.Understood, your a pro, and know your industry. Those wood boiler are a different animal. I will say you may not have the authority to stop a dangerous situation. But I would document the condition and alert the owner. When something happens you are the pro. You can a will be dragged in.
Good lord, what are they burning? I'd be concerned if I had more than 5 quarts, even with an old stove.