While you consider the content think also about the format.
Clear and unambigous langauge to make your pont(s).
Use charts and tables if they help, but they are not adornments so don't feel obliged to include them.
Reference external sources of information etc as foot notes or endnotes
Take each key issue; explain what, why, how, how much, and what next. In other words, justify your proposal, explain what is to be implemented or changed, and why. Explain how it will be achieved; how it fits into the organisation; what the collateral effects will be; what it will cost; what the benefits are (immediate, mid-term, long-term; how it will be monitored and what the on-going costs will be; what might be the consequences of not doing this, and what the alternatives are.
Don't get bogged down in hypothetical arguments - if we were to have two fatal accidents in 150 years..... Stick to common or frequent events to show how change might be evidenced.
Show the impact on productivity or costs as improvments, or as potential losses avoided by reduction in accidents, lost time injuries, staff moral, insurance costs, hassle from HSE etc
Is their a link to staff training, awards and acheievements. ie, is there going to be some output that earns an award, they look great on the MDs bookshelf and all of the company literature.
Include an executive summary comprising bullet points of key issues
Use logical subheadings to break up and give order to the body text
If you have the luxury of time, set it aside then read it again after a day or two. You might at that stage see lots that could, perhaps should, be rewritten to clarify your message
However much you have written, reduce it by half!
Put your name on it - if it's good, make sure they all know who the best ideas came from!
Good luck