Beginner’s Guide: Maximum Arresting Force

Maximum Arresting Force (or M.A.F.) is a term you will hear frequently used in association with fall protection, so it’s better to understand the term before you encounter it (if you’ve already encountered it, better late than never!).  In simple terms, M.A.F. is exactly what it sounds like: the maximum amount of force produced on your body as your fall is being arrested.  The two situations in which M.A.F. will come up most often are when you are discussing the capability of your personal fall arrest system -- What is the M.A.F. on your body if you fall using our product? When discussing regulatory requirements-- What is the M.A.F. allowed on the body by OSHA or as recommended by ANSI (American National Standards Institute)?

Regulatory Requirements

The regulatory requirements are pretty straightforward:  OSHA requires that M.A.F. be limited to 1800 lbs. of force on the body in a fall when wearing a full-body harness, or 900 lbs. of force when wearing a body belt. However, in 1998, OSHA prohibited the use of body-belts with fall arrest systems. So, the magic number is 1800 lbs. of force. 

How do you meet these regulatory requirements?  By selecting the proper equipment and then using it as directed by the manufacturer.  The manufacturer will design their product and test it in accordance with ANSI Z359.  The tests are to ensure that the product keeps the M.A.F. below the regulatory limits.  Once a piece of equipment hits the market with the ANSI Z359 marking, you can rest assured it will be compliant – IF you use it properly.  For example, the OSHA regulations require that a personal fall arrest system (PFAS) be rigged so that the user’s free fall distance is no greater than 6 feet.  When the manufacturer tests the product, they will do so in a way where the user’s free fall distance is no greater than 6 feet.  As long as you, the actual user, then do the same, the M.A.F. will be less than 1800 lbs. of force.  However, if you connect to an anchor at your feet with a 6 foot lanyard with a deceleration device, your freefall will be 6 feet PLUS the distance between your D-ring and your anchor point.  This added free fall distance could increase the M.A.F. beyond the regulatory limit as well as beyond what your body can safely absorb.

Reducing Forces on the Body

That is what this is all about.  How much force can your body safely absorb?  Are you really “saved” from a fall if the arresting force just caused your ribs to puncture your internal organs or caused your spine to snap?  By using the equipment as intended and staying within regulatory limitations, you are protecting your body and well-being. 

So, how is arresting force limited?  First, as mentioned above, is the freefall distance.  Equipment, rigged properly, will keep your freefall distance below 6 feet (with some exceptions which I will get back to in a moment).  For the most part, your vast majority of lanyards with deceleration devices are 6 feet or less in length.  You can further reduce the force on your body through the selection of an anchor point.  The higher your anchor point, the less free fall you have which results in less force on the body.  Regardless, of where you tie off, though, a fall will cause your lanyard to extend its full length (if it doesn’t, then that means you struck a lower level first and were not wearing the proper fall protection to begin with).  Once a lanyard extends to its full length during a fall, a deceleration device kicks in and you are no longer free falling.  An example of this device is rip-stitching.  This deceleration device is webbing stitched together to act as an energy absorber.  As the force of the fall hits the device, the stitching begins to rip.  Each ripped stitch absorbs energy, thereby directing force away from your body and into the device.  Stitches will continue to rip until you’ve slowed to a stop. 

Other devices used to keep your free fall below 6 feet could be rope grabs or SRLs (Self-Retracting Lanyards).  There are some exceptions, though, so make sure you are reading product descriptions and labels before purchasing.  For instance, a lanyard exists that allows for a 12 foot free fall.  This was created for the purpose of tying-off in a situation where the only available anchor point is at your feet (think of an ironworker on the uppermost steel of a building under construction).  While this free fall distance is greater than 6 feet, the lanyard is designed in a way that still keeps the M.A.F. on the user at less than 1800 lbs. of force.

Staying compliant and keeping yourself safe by ensuring your M.A.F. does not exceed safe limits should not be all that difficult to do.  Make sure you are using trusted brands of fall protection equipment, make sure they contain the ANSI marking, and make sure you are using the equipment as the manufacturer requires.  There is no crazy math, science, or voodoo needed to be done on your part – the manufacturers, OSHA, and ANSI have taken care of all of that for you.