1. Your own documents may incriminate you
Documentation is evidence of due diligence. It is not due diligence in itself. Done properly, it helps you prove your case. Done badly, it can incriminate you.
For example, if your health and safety policy says PPE training happens twice a year and you last trained workers two years ago, you have shot yourself in the foot. As Strahlendorf puts it: "If you can't do it, don't say you're going to do it. If you say you're going to do it, then watch yourself and ensure that you do it."
2. Informal, inconsistent practices are not procedures
An unwritten, informal practice, however good, won't save you from prosecution. A judge wants to see your informal best practices turned into formal, written procedures.
3. General due diligence is not specific due diligence
Having an established occupational health and safety management system doesn't mean you have due diligence covered. Courts often require you to prove due diligence related to the specific incident and offence. If the charge is about failing to make sure workers used proper personal protective equipment, you must show due diligence on PPE training for workers.
4. Someone knew about the hazard and didn't say anything
Create an environment that encourages workers to tell you about hazards. If someone knows about a hazard and isn't telling, that can still count as the employer's knowledge. Create opportunities to draw that information out of people. Even a well-developed OHS system can be brought down by one person's knowledge that never reached the employer.
5. No loose ends
Whether the work is done by your own employees or by contractors and their employees, always verify that it has been done. Simply hiring a "competent person" is not enough to prove due diligence. You need methods and systems to verify they did the job they were supposed to do.