Safety plate cacluations

Hello all,
Let me preface this by saying I am not an engineer or studying to be one. Your craft is well beyond my mental grasp. I am a safety manager who works for a construction company. I am trying to mitigate risks on my jobsite and make sure everyone goes home safe. My current issue is hole covers. Industry standard is to use either plywood job built covers or plastic purchased one. Neither are great for the task. The wood has strength, susceptible to water, and its a trip hazard due to its thickness. I have designed a steel hole cover for my company that our yard is going to manufacture for round holes, conduits, and chases up to 6" in diameter. This is with 3/16" steel with welded chunks of scrap pipe on the underside to keep it on the hole. My next issue and why I'm asking you for your knowledge is bigger hole, Square holes, block outs. Basically my concern is anything big enough to drop a wheel of a scissor lift into. A scissor lift is a mobile self erecting scaffolding. These machines weigh roughly 2900lbs. They are on 4 wheels. I would like to use 1/4" plate steel I think to be able to lay into square and rectangular openings. The trouble I am having is figuring out what the max size of hole I could safely cover with these steel plates. Meaning how big of hole could I cover with 1/4" steel plate and be able to drive a scissor lift on to. I think only one wheel would ever be able to get on there at a time. Safety factor of 4. On the under side would welding angle iron across its span or angle iron in a honey comb pattern help strengthen the cover at all? Thanks for any help.
Cheers,
Kyle