ExposureBlog

My good friend and former DOE safety guy/motorcycle maven Gary Noss sends along two great articles on how to lift a motorcycle that has fallen over, here and here.  I used to ride one and will likely do it again, so for me anyway, this is timely.   

It’s not every day that you find new info about friction–you know–that ill-defined resistive force that occurs when you rub two surfaces against each other. 

Lawyers who deal in slip and fall cases can probably recall the safety guy dragging the exemplar shoe across the vinyl tile at K-mart.  The shoe was likely attached to a spring with a kind of device that looked like a horizontal fish scale.  It was supposed to measure drag and thus, well, coefficient of friction.  Anything less than 0.5 was bad. 

Well, if you’re one of those lawyers, this one’s for you.  It seems that the definition of friction has been enhanced.  We now know the minimum distance for friction to occur—about a nanometer.  And now we also know that friction is dependent upon the chemistry of the materials involved.

Okay. That much we all knew anyway.  Tennis shoes seem to have a higher coefficient of friction than flats.  Can’t dance in tennis shoes.  No slide.

Back to the serious stuff.  Now it seems that two objects don’t even have to be in that close contact to create friction.   The official term is friction at a distance, but the distance is still too small for the average jury to see—even with bifocals.  The distance is just a little greater than a nanometer.  Not like twenty feet or something.  Read all about it here.

I get a lot of calls about slip-and-falls.  While some lawyers consider a slip-and-fall case a walk in the park (so to speak), safety guys generally have a different view.  That view can be expressed as this:  most of them are complicated and the answer isn’t as clear as everyone thinks.   Lawyers for example, like to think that a little water on a vinyl floor is all it takes.  Well, sometimes that’s the case.  And sometimes it isn’t.  I’ve been involved in a few cases where the slip wasn’t a slip at all, but a trip. Big difference.  Typically, if the victim falls backward, it’s a slip.  If the victim falls forward, it’s a trip.  Backward: slip. Forward: trip.  Pretty simple.

Or not. 

Sometimes, things get weird, like when the middle-aged lady in the retail store suddenly started skating along the floor like there were ball bearings on her shoes.  This was before the skate-tennie was invented, so we ruled that one out pretty quick.  The plaintiff’s counsel, an old, experienced wardog of a lawyer had it figured out: “the floor,” he told me “had too much wax on it.  Way too slick.”

Actually, under certain conditions, wax will actually slow you down. It’s complicated. 

I inspected the place, and the floor looked fairly normal.  And there was no water around to spill.   Then one of the cashiers happened to remember that the week the accident happened, the store was selling houseplants in the area.  Had a little table covered with houseplants. . .that were watered regularly to make them look nice.  Fine. Now we had the water.  But again, water wasn’t going to do it alone.  Was there something about the plant itself?  One of the cashiers had remembered having problems with kids coming along, picking parts of the houseplants and throwing them on the floor.

I dug out my old botany textbooks.  It seems the stems of plants are composed of several layers of cellulose over regular cells that contain–among other things—oil.  A plant stem removed from the rest of the plant begins to decay pretty quickly and, especially in water, turns into a gooey mush that includes a mixture of water and oil—just like you find in a bottle of Italian salad dressing.  Shake it up and the oil in the water forms beads.  Like tiny ball bearings.  And another thing—the stem, made of cellulose, is usually the last to go bad. 

So here was a plausible model—a couple of plant stems and stalks lying on the floor—maybe in a puddle of water.  No obvious danger.  But on closeup, the stems were essentially like paper soda straws filled with salad dressing. 

Ever see those pats of butter in the cafeteria?  The ones with the butter sandwiched between a piece of glossy cardboard and thin paper?  Between a shoe and a hard floor these little guys act like cheap skates.  They actually get you moving more quickly than cheap skates.  But with less control.

Okay. Based on the evidence it seemed that the stems and stalks on the floor acted like that pat of butter.  If someone stepped on them properly, they would suddenly find their foot was propelled forward by thousands of tiny little balls of plant oil.

The defendant made a settlement offer (during trial) and the plaintiff accepted.  After that, the store solved the deadly houseplant problem by restricting sales of its plants to the garden area behind the building.