It never ceases to amaze me the types of issues that you come across on construction sites. Above is are two examples of wholly inadequate protection of open manholes. Both were positioned adjacent to heavy foot and vehicle traffic. I would hate to think what could possible have occurred if a vehicle wheel or track, let alone a person, had fallen into either manhole.
Below is a great example of a great bit of kit from Protec (http://www.protection.co.uk/blog/products/hi-vis-manhole-protector-customer-review/). Makes the hazard clearer and highly visible.