Ladder Safety Packet Overview

  

This module has been created for use in a statics course as a case study to show the need for engineers to take a holistic view of their projects, especially where safety is involved.  The ladder case study should follow a block of instruction which develops concepts of dry friction.  It is ideal for presentation after an examination review when the students can relax without concern for homework requirements.  A lecture outline is presented that discusses the basic rules of ladder safety and design.  A three part example is also featured.

  

Time for presentation is estimated as 40 minutes. 

  

Objective:

           

1.         To introduce engineering students to safety aspects in design.

2.         To increase awareness of basic ladder safety and design associated with ladder use.

 

This packet includes the following items:

 

·         Preview the Lecture material for the instructor

·          Preview the Overheads for use during the lecture

·          Preview the Ladder Example Problems

Copies of the case study may be made to give to the students if the instructor desires.

 

Download the full Ladder Safety Module in printable Adobe Acrobat Format (pdf).  This includes overheads in a ready to use format.

 

Ladder Safety Lecture Outline

 

The Five Rules of Ladder Safety (OVERHEAD 1)

According to the National Safety Council, falls are the leading cause of death in and around the home. 

Over 6000 people die from falls at home each year. 

These accidents include slipping on wet or icy surfaces, falling down stairs, falling off the roof, and falling from ladders.

More than 30,000 people are injured each year by falls involving ladders.

Many of these accidents can be prevented by following the five rules of ladder safety.

 

There are five basic rules that should be followed when using a ladder.  (OVERHEAD 2)  They are:

RULE 1: Select the right ladder for the job.

RULE 2: Inspect the ladder before you use it.

RULE 3: Set up the ladder with care.

RULE 4: Climb and descend ladders cautiously.

RULE 5: Use common sense when working on a ladder.

Engineers can design ladders to be inherently safer, thereby reducing the risk of injury to ladder users. 

 

(OVERHEAD 3)

The ladders should be constructed of appropriate material for the application for which the ladder will be used.

Ladders can be manufactured from wood, aluminum, or fiberglass, and be designed for light to industrial use.

Be sure the ladder is long enough for the application and sturdy enough to withstand repeated use.        

Aluminum is lightweight and is not affected by weather as much as wood.

Wood and fiberglass ladders are not as “shaky” as aluminum ladders.

If the work involves possible contact with electricity, be sure to construct the ladder of wood or fiberglass.

Design stepladders to have spreaders that can be locked in place and that the ladder has safety feet which will provide more stability and reduce the chances of the ladder slipping while in use.

 

(OVERHEAD 4)Apply a slip-resistant material to the steps of a metal ladder to provide better footing if needed.

 

(OVERHEAD 5)  Design straight ladders to be used at a four-to-one ratio.  The base of the ladder should be one foot away from the wall for every four feet of height to the point of support.  Stickers can be placed on the ladder showing the angle at which the ratio will be achieved.  (Make sure stickers are applied correctly!)

 CASE STUDY (See following sheets.)

This multi-part example shows how the angle of a ladder can affect the forces involved in ladder usage.  No overheads are provided for this portion as it is assumed that the problem will be worked on the board.  Students may be given copies of the problem if the instructor wishes.                       

  

Lecture adapted from http://www.cdc.gov/niosh/nasd/docs2/as58500.html

Overhead 1

The Five Rules of Ladder Safety

According to the National Safety Council, falls are the leading cause of death in and around the home. 

  ·                    Over 6000 people die from falls at home each year. 

  ·                    These accidents include slipping on wet or icy surfaces, falling down stairs, falling off the roof, and falling from ladders.

  ·                    More than 30,000 people are injured each year by falls involving ladders.

  ·                    Many of these accidents can be prevented by following the five rules of ladder safety.

 

Overhead 2

THE 5 RULES OF LADDER SAFETY

  RULE 1: Select the right ladder for the job.

  RULE 2: Inspect the ladder before you use it.

  RULE 3: Set up the ladder with care.

  RULE 4: Climb and descend ladders cautiously.

  RULE 5: Use common sense when working on a ladder.

Overhead 3

LADDER DESIGN CONSIDERATIONS

 

The ladders should be constructed of appropriate material for the application for which the ladder will be used.

 

Design stepladders to have spreaders that can be locked in place and safety feet which will provide more stability and reduce the chances of the ladder slipping while in use.

Overhead 4

LADDER DESIGN CONSIDERATIONS

 Apply a slip-resistant material to the steps of a metal ladder to provide better footing as needed.

Design straight ladders to be used at a four-to-one ratio.  The base of the ladder should be one foot away from the wall for every four feet of height to the point of support.  Stickers can be placed on the ladder showing the appropriate angle at which the ratio will be achieved.

Overhead 5

The base of a straight ladder should be the length of the ladder divided by four.  (A one-to-four ratio.)

LADDER EXAMPLE PROBLEM

            Given:  

            Ladder Length = 20 ft (neglect friction at ladder/wall interface)

            Ladder Weight = 50 lbs

            Person Weight = 200 lbs at 16 ft up the ladder

 

We know that the maximum angle for safe operation is 75.5o, which provides the desired four-to-one height to ladder base offset distance.

 

FREE BODY DIAGRAM (Neglect friction at ladder/wall interface)

 

 

 

Labels are applied so that when the ladder is at the appropriate angle, the label is perpendicular to the ground. 

 

Substituting in P = 200 lbs and W = 50 lbs:

 

        Fwall = Ffriction = 47.84 lbs

        N = P + W = 200 + 50 = 250 lbs

  (We’ll assume that the friction force and the normal force are approximately equal, and the ladder could move at any time.)

 

In the desired case: 

If fall were to occur:   

 

If the label was applied incorrectly, what might happen to the person?  (The ladder would be misaligned with the floor, and the person could be injured if the ladder falls.)

 

Let’s assume off by 1o, so the base angle is 74.5o:

 

 

This value is greater than the Fwall maximum found earlier to be 47.84 lbs.  The ladder would fall in this situation.

 

PART 2

Let’s look at another situation.

            Ladder = 20.3 ft long

            Ladder = 50 lbs

            Person = 200 lbs

 

Substituting in P = 200 lbs and W = 50 lbs gives Ftree = 47.23 lbs.

(This is the maximum force that can be exerted by the tree without the ladder slipping.)

 

at 70.5o: Ftree  = 64.7 lbs

at 65.5o: Ftree  = 83.23 lbs

 

Changing the weight of the ladder to 30 lbs:  What base length (x) is required?  What is the new Ftree ?

 

          x = 5.08 ft

 

 

Substituting in P = 200 lbs and W = 30 lbs gives Ftree = 44.65 lbs.

 

From these examples, the importance of having the ladder at the proper angle can be seen.  The ladder labels provide help in achieving this angle, but cannot always be relied upon, as errors are possible in the label application angle.  Even small variances in the angle can lead to fall of the ladder, and may result in injury to the people using the ladder.