Confined Space Lesson 8: RESCUE EQUIPMENT INSTRUCTIONAL GOAL Upon completion of this topic, the student will understand the need to properly select and use rope-rescue equipment for confined space entry and rescue. ENABLING OBJECTIVE Based on the information presented in the classroom and in the student guide, the student will be able to: 1. Explain the uses and limitations of static kernmantle rescue rope. 2. Identify various rope rescue hardware components and explain their use. 3. Demonstrate the correct procedure for tying the following knots and hitches: a) Simple figure-8 knot b) Figure-8 on a bight knot c) Figure-8 follow-through knot d) Figure-8 bend e) Clove hitch f) Munter hitch g) Double fisherman‘s knot h) Bowline knot i) Butterfly knot OVERVIEW This chapter provides information on different types of rope rescue equipment that can be used in confined space entry and rescue. Proper use and care of the equipment as well as any limitations that the user should be aware of will be covered. ≤HMTRI 2004 Page 49 Confined Space Rescue Ropes, W ebbing, and Equipm ent The 1990 revision of the NFPA 1983 Standard on Fire Service Rope Life Safety Rope, Harness, and Hardware states that a life safety rope shall have a maximum working load of not less than 300 pounds for a one-person rope and 600 pounds for a two-person rope. It further states that the minimum breaking strength shall not be less than 4,500 pounds for a one-person rope and 9,000 pounds for a two-person rope. Rope Strength At first glance it may seem odd as to require a breaking strength of 4,500 pounds for a one-person rope. Common sense would indicate that a person would not be suspended on the rope with 4,500 pounds, but the possibility of the rope needing to withstand 4,500 pounds of force is a real possibility. Force, simply defined, is anything that can cause a moving object to change its shape, change its direction of motion, and/or change the speed at which it is moving. As an example, you apply forces to your car when driving. Every time you step on the accelerator or the brake, you change the speed of your car. Likewise, when you turn a corner, you change direction. If you collide with something, you change the shape and speed or even direction of your vehicle. The force that causes these changes is called Cinetic energy. Kinetic Energy Kinetic energy is expressed mathematically as KE = ² mv2 where m is the mass (weight) of the object and v is the velocity (speed) that the object is moving. It should be apparent that the larger the mass of an object, the more kinetic energy it will possess, assuming that the velocity remains constant. This is easy to see when comparing the stopping distance for a car traveling 60 mph with the stopping distance of a freight train traveling 60 mph. The relationship between mass and kinetic energy is a linear 1. That is, if the velocity is held constant and the mass is doubled, the KE is doubled; if mass is tripled, the kinetic energy is tripled, and so on. Free-fall is different. An object in free-fall, such as when a person slips in a confined space vertical entry, will accelerate at a constant 32 feet per second for every second of fall (32 feet/second2) because of the force exerted by gravity. W hat this means is that acceleration changes the velocity, so the velocity is no longer constant. However, the mass of the falling object does remain constant. By looking at the mathematical expression for kinetic energy, KE = ² mv2, it should ≤HMTRI 2004 Page 50 Confined Space be noted that as velocity doubles, the KE quadruples (increases by four times) since the velocity in the expression is raised to the second power, or "squared" (v2). Subsequently, if the velocity triples, the kinetic energy increases by a factor of 9. The following table shows the relationship between distance and time of free-fall and the kinetic energies generated: Kinetic Energy Chart for a 160-Pound Falling Body Height of Fall Time of Fall Velocity of Fall KE or Force of Impact (feet) (seconds) (feet/second) 2 (pounds) 10 0.80 25.6 1,638 20 1.10 35.2 3,097 30 1.40 44.8 5,017 40 1.60 51.2 6,553 50 1.78 56.9 8,410 60 1.95 62.4 9,732 70 2.10 67.2 11,287 80 2.25 72.0 12,960 90 2.38 76.1 14,477 100 2.50 80.0 16,000 As stated earlier, a rope must absorb the force of a falling object in order to stop its fall. According to the data table, it does not require much falling distance to generate 4,500 ft/lbs of force. A person weighing 160 pounds (not including equipment) in falling only 1.4 seconds would require a rope to withstand 5,017 ft/lbs of force. If this person fell 75 feet, a speed of nearly 50 mph would be attained and they would impact with a force of almost 6 tons! Consider the act of jumping from a chair onto the floor with your knees locked and landing flat-footed. The jar or jolt received upon impact with the floor is rather large because the collision is non-elastic. In other words, the energy of impact was dissipated in a very short period of time. However, if the jump is repeated with knees bent and landing upon the balls of the feet, the impact jolt is reduced since the collision time is increased. It is for this reason that the dashboards of cars are made of foam rubber rather than steel. The "give" in the foam allows the force of the collision to be dissipated over a longer period of time, reducing instantaneous kinetic energy. This same principle is applicable to rope work when friction devices or brakes are used to gradually slow a fall rather than stop it with a jolt. By lengthening the time of deceleration, the force that the rope must absorb at any one instant is kept fairly low. More importantly, ropes stretch. The NFPA Standard indicates that a lifeline breaking elongation shall not be less than 15 percent or more than 55 percent. Stretching the rope is another way of spreading the shock energy over a longer period of time. This advantage is not present in cable systems. ≤HMTRI 2004 Page 51 Confined Space W ork, Mechanical Advantage, and the Pulley The pulley is one of six simple machines with particular application in confined space entry and rescue. Basically, the pulley is used to do two things: (1) change the direction of a rope‘s force, and (2) produce mechanical advantage. To understand the concept of mechanical advantage, one needs to look at the definition of work. In science, work is defined as the product of force and distance and can be expressed mathematically as shown here: W ork = Force x Distance For example, it takes force to push a refrigerator across the floor. The farther it is pushed, the more work it will take. If you have a 120-pound weight that needed to be lifted 2 feet, that would require: W ork = Force x Distance = 120 lbs x 2 ft = 240 ft/lbs. If you had a pulley attached just above the weight and a rope was strung through the pulley and attached to the weight, by pulling the rope 2 feet, you could lift the weight 2 feet. This would be equivalent to 240 ft/lbs of work. The pulley only changed the direction of the rope. It did not offer any mechanical advantage. Suppose that you now have a two- pulley system where one pulley is anchored above the weight, and the other pulley is attached directly to the weight. W hen the rope is pulled this time, the pulley attached to the weight moves. Moving pulleys provide mechanical advantage. In other words, the 120-pound weight will not feel as heavy because of the mechanical advantage that the moving pulley provides. How much lighter will it feel? Since you now have a 2:1 (pronounced two-to-one) mechanical advantage system, the weight will feel one-half as heavy. How can the presence of a moving pulley reduce the apparent weight of this object? The answer lies in the mathematical definition of work. Notice that if you raise the weight 1 foot using a 2:1 system, you will have to pull 2 feet of rope through the pulley system. So, to lift the 120-pound weight 2 feet, you will need to pull 4 feet of rope through the system. This is expressed mathematically as: W ork = Force x Distance = 60 lbs x 4 ft = 240 ft/lbs Note that you still had to supply 240 ft/lbs to lift the weight 2 feet. Consequently, no matter how you get it there, lifting the weight 2 feet is going to require the same amount of work. W hat is variable is how long you spread that work out. Instead of doing all of the work through 2 feet of rope, you do the work over twice the time. Therefore, you would only have to supply half the effort at any one time. It's like loading a piano into the back of a truck. You can apply a lot of force in a short time and lift it straight up or apply less force at any one time by using a ramp and spreading that same amount of work over a longer period of time.