How many jobs have you done where you needed to spread plastic on the ground to work, and needed to walk on that plastic?  If you have done it, you may know where this conversation is going.  Plastic is not the best material to be standing on especially when it gets wet (remember the old slip and slide).  The surface turns into a slippery “ice” like surface creating a severe slipping hazard.  There are several ways to mitigate the slip hazard such as spreading some soil over the plastic to create some traction, placing wood or pallets on the plastic to create an elevated platform (mind the gap when using pallets).  What other ideas do you have to mitigate slipping when you must stand on top of plastic?

How about this scenario, you need to double up the sheets so there are now two stacked sheets under your feet.  Now we have added a second slip plane where the sheets themselves move independently and creating additional traction on the top surface (like soil) is not going to mitigate the slipping hazard.  The underlying question here is why do you need two layers?  You probably don’t and should never walk atop folded layers of plastic sheeting.  The solution, use a thicker single sheet of plastic. 

Thirdly, plastic spread on the ground has a tendency to curl at the edges especially under a very slight breeze creating a tripping hazard where you step onto the plastic.  If you are doing work where people need to transition on and off the plastic, plan accordingly and engineer a solution that keeps people from tripping.