While step ladders are really useful, there are many factors that can lead you to fall off a step ladder. Here are 13 of them:
1) Rickety Ladder: The step ladder is in old and in poor shape because its joints are worn. This makes rickety so that the step you are standing on can suddenly shift as you begin to reach for something.
2) Your Center of Gravity moves outside the ladder Base of Support: You will fall for sure if your body's center of gravity moves outside the ladder's base of support defined by the area between its four feet. (Your center of gravity is defined as the line from your body's center of mass to the center of the earth). How can this happen? Say the step ladder is positioned on ground that slopes downwards to the right. This means that the further you climb up the ladder, the more your body's center of gravity will move to the right relative to the ladder.'s base of support The ladder will become unstable and tip you into a fall to the right once you have (a) either climbed so high that your body's center of gravity lies to the right of the feet of the ladder, (b) you stand to the extreme right of the step you are standing so as to place your center of gravity outside the ladder;s base of support, or (c) you lean so far to the right to grab or lift something that your body's center of gravity moves beyond the ladder's right feet. This is why step ladders are designed with feet that splay out from the top to give you a large base of support.
3) Poor Ladder Rigidity to Side Loads: Surprisingly, there are no safety standards on how rigid a step ladder has to be to resist forces you exert to the left or right when standing on the ladder (https://www.ncbi.nlm.nih.gov/pubmed/15970205). Some ladders are well built and are really rigid. Others are cheap and deflect too much laterally when you push on something to the left or right: if you push to the right, they deflect to the left, and when you pull towards you on something on your right, they deflect too much to the right. This can do two things. First it can bring your body's center of gravity outside the ladder's base of support and the ladder will then tip you in that direction. Or it can start an oscillation of the ladder making the step you stand on wobble left and right. Unless you have something sturdy to hold onto, you can lose you balance trying to counteract that wobble and then fall to the left or right because you under- or overcompensate. This is more likely to happen in the dark (for example, while hanging holiday lights) because you no longer have the good visual cues that help you balance in a well lighted situation. (Your brain uses cues from your vision, from your inner ear [vestibular organs] and from thousands of sensors in your muscles, joints as well as the skin under your feet to help you balance. Visual cues are usually a very reliable source of information for the brain - unless it is dark, when those cues are drastically diminished].
4) Adverse Effect of Medications: You are on medications (i.e., benzodiazepine, anti-cholinergic drugs) that slow your reactions or decision making, or you have alcohol on board. These will slow your balance recovery responses to a perturbation of the ladder that you cause yourself just by making a sudden movement. That sudden movement can cause the step you are standing on to shift to the left or right causing you to lose your balance because your reactions are just to slow to save yourself.
5) Adverse Effect of Medical Conditions: You have a medical condition that prevents you from feeling what is happening to the step you are standing on when it suddenly moves to the left or right. An example would be diabetic peripheral neuropathy that decreases your ability to sense changes in pressure or movement under your feet, and thereby slows your reaction time as you attempt to recover your balance.
6) Moving Too Quickly: You may not appreciate that if you make a sudden move to the left or right, or you take a sudden step to the left or right, Newton's law specifies that you will push the step you are standing on in the opposite direction - whether you like it or not. The faster you accelerate your body part to move quickly, the larger that destabilizing force is on the step you are standing on. This sets up a left-right structural vibration of the ladder making it wobble under you. If your balance recovery isn't good enough then you can fall to the left or right as you try to recover. This problem gets worse (a) the higher you stand on the step ladder, (b) the higher the step ladder is, (c) the faster you make the movement, and (d) the heavier the body part that you accelerate rapidly. Moral of the story: always move slowly and deliberately on a step ladder, and never hurry!
7) Overreaching: If you reach far to the side and then rest your hand on that object to check something, but all of a sudden that object gives way or shifts, your center of gravity may lie outside the ladder base of support causing you to fall in that direction. The ladder will fall in the opposite direction, not helping your recovery. Moral of the story: if you have to over reach to the side, get down and move the ladder closer. Don't be a fool and overreach!
8) Pushing/Pulling Too Hard Laterally: We have published biomechanical studies on factors causing step ladder instability (https://www.sciencedirect.com/science/article/pii/S0003687005000438?via%3Dihub) that show that one should limit the force you generate to the left or right when using a tool like a drill to about 8% of your body weight so as to not destabilize the ladder. Ladder stability was three times more sensitive to the height of the tread you stand on than to where you stand on that tread. So be extra careful on high step ladders!
9) Something Loose Under One Ladder Foot: If you pitch one of the feet of the ladder on a loose stone without noticing it, the stone can move as you work on the ladder causing the ladder foot to move, thereby moving the ladder rung you are standing on. If you are not quick enough to recover your balance, then you can fall.
10) Unseen Soft Spot Under One Ladder Foot: You are in a hurry and you set the step ladder up on uneven ground covered with vegetation without noticing a soft spot under the ladder's rear left foot. You climb up the ladder, but happen to climb on the right side of all the ladder's steps because your task is on the right side of the ladder. Your body's center of gravity stays within ladder's base of support this time defined defined by the two right legs and the front left leg - so the ladder seems stable while you work. But, when you are finished you move to the center of the ladder step on which you are standing to admire your work. That places weight on the rear left leg that now sinks into the mud tipping the ladder (and you) backward and to the left when you were least expecting it. Unless you have quick reactions and good balance, you may fall.
11) Adverse Effect of Age: You are getting older. You have many years of experience in using step ladders. But, even if you are totally healthy, at the age of 70 years our research has shown that you have 25% less muscle strength and 40% less muscle power (ability to move a weight or body segment rapidly) than you had when you were 20 years of age. Our research has shown that these losses of strength mean you don't have as quick reactions as you used to and your ability to move body segments quickly is definitely adversely slowed. So, even if you feel like you are 20 years of age, your body is a far cry from what it was. Add to that any neural, muscular or bony impairments you may have accumulated and they will further adversely affect your ability to recover your balance on the ladder. Finally, if you fall, your decreased muscle and bone strength mean that when you hit the ground your fall-related injury is going to be more severe than if you were 20 years. Moral of the story: find another way to get the job done!
12). Standing Backward on a Step: You climb the ladder normally, facing towards the step ladder. But when you get to the right height, you turn 180 degrees to face away from the ladder in order to reach your work. As you work you absent-mindedly off load one foot because it's getting tired. You put that foot back down on the step again as you turn slightly, but it slips forward off the step, causing you to fall - because there is nothing to grab onto with your hands - no rails, no rungs - just air. There have been worker deaths from this kind of fall from a step ladder. (https://www.youtube.com/watch?v=XXit0ziMIAA).
13: Standing on the Top Step: Don't ever stand on the top step because you can no longer brace yourself against the ladder. A quick movement to one side or the other will create a lateral reaction force between your feet and the top step thereby pushing the ladder over sideways with a lever arm as long as the ladder is high. A custodian fell from the top step of a 7 foot step ladder attempting to clean a middle school window 15' off the ground: https://www.cdph.ca.gov/Programs/CCDPHP/DEODC/OHB/FACE/CDPH%20Document%20Library/16CA006.pdf