Hazard Control PDF

Hazard Control Hazard control involves eliminating or reducing the risk resulting from a hazard Planning vs Design Planning is the process of developing a method for achieving something Designing is an extension of planning that incorporates more detail and specific inform...

Hazard Control Hazard control involves eliminating or reducing the risk resulting from a hazard Planning vs Design Planning is the process of developing a method for achieving something Designing is an extension of planning that incorporates more detail and specific information Design errors can lead to hazards, such as failure to convert square inches to square feet or failure to include a factor of safety in a structural calculation Hazards in Production and Distribution Hazards can result from production and distribution activities, such as replacing one chemical with another that introduces toxic or flammable hazards Inadequate packaging can result in the release of hazardous materials to handlers, distributors, or buyers Hazards in Maintenance and Repair Hazards can result from insufficient, delayed, and improper maintenance and repair Failure to tighten a bolt or tightening it too much can create a hazard Failure to lock out or provide lockout devices can also introduce hazards Communication The four components of communication are sender, message, media/channel, and decoding, receiver, and feedback Poor communication or failures in communication can introduce hazards After an accident, alcohol tests should be conducted within 8 hours, and substance tests should be conducted within 32 hours Drivers should be subjected to random/unannounced tests for alcohol and drugs Measurement Tools Slip meters are used to measure the slipperiness of a surface and determine the friction coefficient Light meters are used to measure the illumination Accident Causes Direct causes of accidents include energy sources and hazardous materials Indirect causes of accidents include unsafe acts and conditions  Basic causes of accidents include management policies, personal or environmental factors Mechanics and Structures Important properties of materials include strength, brittleness, ductility, thermal expansion and contraction, shape, age, exposure to environmental conditions, and exposures to chemicals The safety factor (SF) refers to the ratio of a failure-producing load to the maximum safe stress a material may carry Falling object protection systems (FOPS) are designed to prevent objects in a load from penetrating into the operator compartment Cranes and Safety Devices Cranes may have built-in safety devices or warning devices, such as load-indicating devices, limit switches, boom angle indicators, and load-moment indicators Basket hitch distributes the load by half on each sling, while a choker hitch sling carries the same load, but the load is carried by a single vertical element Elevators, Escalators, and Manlifts These devices must be maintained regularly and inspected by trained people Design standards incorporate safety features like brake systems, automatic braking if a cable fails, double doors for the car and openings, interlocks on all doors, and access doors with detector switches Elevators must contain emergency alarms and means of egress Transportation 37% of motor vehicle deaths occur between 10:00 p.m. and 4:00 a.m. The death rate per crash generally increases with age Distractions like cell phones, global positioning displays, video and DVD players, and other built-in or driver-carried equipment can contribute to accidents Accident Reconstruction S = V2/30 μ, where S is the distance, V is the initial velocity, and μ is the coefficient of friction for the tires on the pavement Railroads Hazards in railroads include explosions, fires, and releases of toxic materials Most rail deaths and injuries result from grade crossing accidents with motor vehicles Controls include barrier gates and signals, thermally insulated tank cars, and sensors that detect the speed of a train Aviation Hazards Leaking fuel tanks and ignition can be disastrous Icing of wings and loss of lift is still a danger in severe weather Designing emergency exiting for as many as 450 passengers is a challenge Detecting and avoiding wind shear, particularly in clear weather, also remains a challenge Pipelines Hazards Hazards are related to materials handling and excavation during construction Fire and explosion are major concerns for fuels and flammables A leak in a pipe, fitting, valve, pump, or other component of the pipeline could produce disastrous results Transportation of Hazardous Materials The Transportation Safety Act of 1974 regulates the transportation of hazardous materials Hazards include explosives, radioactive material, flammable liquids or solids, combustible liquids or solids, oxidizing or corrosive materials, compressed gases, poisons, and etiologic agents Controls include defining and recognizing hazardous materials, excluding certain materials from particular transportation modes, limiting quantities, controlling placement, design and selection of packaging, labeling of containers, restricting transportation routes, and using shipping manifests, incident reporting, and training Electrical Circuits Resistance in a series circuit: R = R1 + R2 + … Rn Resistance in a parallel circuit: 1/Rt = 1/R1 + 1/R2 + 1/R3 + … 1/Rn Voltage and Power in AC and DC Circuits Voltage in AC circuits: V = √PI/CosΦ, where V = voltage, I = impedance (Ω), and ϕ = phase angle in degrees Power in DC circuits: P = VI, where P = power (W) and 1hp = 736 W Power in AC circuits: P = V² CosΦ / R, where P = power (W), V = voltage, CosΦ = power factor, and R = resistance Resistance in DC Circuits Resistance in DC circuits: R = ρ L/A, where R = resistance, ρ = resistivity of the metal (intrinsic ability to resist the flow of electricity), L = length (m), and A = cross-sectional area in square meters Joule's Law  Joule's Law: P = I²R = IV = V²/R, where P = power (W), I = current (A), R = resistance (Ω), and V = voltage (V) Capacitors and Inductors Capacitors: passive electronic components consisting of a pair of conductors separated by a dielectric (insulator) Capacitance in a series circuit: 1/Ct = 1/C1 + 1/C2 + 1/C3 + … 1/Cn Capacitance in a parallel circuit: Cparallel = C1 + C2 + … Cn Inductors: passive electrical components that can store energy in a magnetic field created by the electric current passing through it Inductance in a circuit: measured in Henries (H) Oscillators and Thermocouples Oscillators: electronic circuits designed to produce high-frequency alternating currents Thermocouples: sensors that measure temperature, consisting of two different types of metals, which convert heat energy into electrical energy Electrical Shock Hazard Electrical shock hazard: severity of injury depends on the amount of electrical current and the length of time the current passes through the body Body resistance, path of current through the body, and other factors affect the severity of injury Different levels of electrical shock: 5 mA (slight shock), 6-25 mA (painful shock), 50- 150 mA (extreme pain), and 75 mA (ventricular fibrillation, potentially fatal) Electrical Fires and Explosions Electrical fires: often caused by defective or misused electrical equipment Class C or multipurpose (ABC) fire extinguishers should be used to extinguish electrical fires Explosions: can occur when arcing in the presence of a combustible atmosphere, and precautions should be taken to prevent ignition Hazardous Locations Hazardous locations: classified into three categories: I (flammable gases or vapors), II (combustible dust), and III (easily ignitable fibers or flyings) Electrical Safety Precautions Rubber pad: used to insulate workers from electrical distribution lines Defective or damaged cords: should be removed from service and proper use of cords should be followed to prevent shocks, burns, or fires  Distance and location: minimum distance required from a floor or walking surface to mechanical power transmission apparatus varies with different standards, often 7 or 8 ft Machine Guarding Enclosure guards: fixed or movable guards that prevent access to hazardous areas of a machine Interlocked guards: shut off or disengage power and prevent machine start-up when the guard is open Limitations: guards may not be practical for changing production runs, machine adjustment and repair may require guard removal, and other means of protecting maintenance personnel may be required Hazard Control Models Many elements are involved in incidents: people, machines, environments, and materials Four Ms: Man, Media, Machine, and Management, and MEEP: material, environment, equipment, and people Goal Accomplishment Model: people perform activities and use equipment to help them, under constraints of physical, social, and regulatory environments Housekeeping and Housecleaning Housecleaning: picking up, wiping up, and sweeping up, including removal of scrap and waste Housekeeping: involves regular maintenance and cleaning of equipment and facilities to prevent hazards and ensure a safe working environment Flexible Cords and Grounding Do not use flexible wiring in areas where frequent inspection is difficult or damage is likely to occur Flexible cords should not be run through holes in walls, ceilings, floors, doorways, or windows unless physically protected Grounding removes charge from equipment, protecting people from electric shock Bonding connects all components, dispensing and receiving containers, to eliminate potential differences between conductors Fuses and Circuit Breakers Fuses are devices that cut off power supply when current exceeds a given value, preventing overload and overheating of electrical wiring Fuses operate within a given time and temperature, but are too slow to protect people from electric shock Circuit breakers are forms of switches that open when current exceeds a designed limit  There are two types of circuit breakers: thermal and magnetic, with varying response to environmental temperature Hazard Control and Models Hazard control may require multiple means of control, as a single method may not be sufficient The four Ms involve: Man, Media, Machine, and Management (MEEP: material, environment, equipment, and people) Goal accomplishment involves people performing activities using equipment in a facility, under physical, social, and regulatory environments, with time and cost constraints Housecleaning and Housekeeping Housecleaning involves picking up, wiping up, and sweeping up, as well as removal of scrap and waste Housekeeping includes removal of materials of construction, P&IDs, electrical classification, and relief system design Process Hazard Analysis An initial process hazard analysis (hazard evaluation) is required on processes covered by the standard The analysis should identify, evaluate, and control hazards involved in the process Various methodologies can be used, including What-If, Checklist, What-If/Checklist, Hazard and Operability Study, Failure Mode and Effects Analysis, Fault Tree Analysis, and an appropriate equivalent methodology Insurance and Other Topics Owners and contractor protection (OCP) protects business/property owners or general contractors against liability due to negligence or independent contractor/subcontractor acts There are four categories of insurance: property (fire), health, liability, and life insurance Construction insurance covers buildings under construction against perils such as fire, wind, and theft CE and UL are product conformity certifications for Europe and the USA, respectively Commercial drivers are subject to specific regulations, including alcohol consumption and reporting requirements Hexavalent chromium is associated with welding stainless steel DOT requires annual random testing of at least 50% of a company's entire fleet for random controlled substances Safeguarding Devices  Presence-sensing devices, such as photoelectric, radio frequency, or electromagnetic devices, attach to the machine's control system to stop operation when the sensing field is disturbed. Presence-sensing mats detect a predetermined weight on the mat to stop the machine's operation. Point-of-Operation Safeguards Two-hand control requires concurrent and continued use of both hands to prevent them from entering the danger area. Two-hand trip requires concurrent use of both hands at the start of the machine cycle to prevent them from being in the danger area. Barrier Guards Type "A" Gate is a moveable barrier applicable to mechanical power presses, providing a barrier between the danger area and the operator until the completion of the machine cycle. Type "B" Gate is a moveable barrier applicable to mechanical power presses and press brakes, providing a barrier between the danger area and the operator during the downstroke. Awareness barriers alert people to a hazardous area or operation, and a warning should explain the machine's hazard and the purpose of the barrier. Hood guard is a circular table saws guard that "floats" vertically as material is moved into the blade. Adjustable and Self-Adjusting Guards Adjustable guards are barriers that adjust for a variety of production operations, but may require frequent maintenance or adjustment and can be made ineffective by the operator. Self-adjusting guards move according to the size of the stock entering the point of operation, but do not provide maximum protection. Restraint and Pullback Devices Restraint devices connect the operator's wrists to a fixed anchor point, limiting their hands from reaching the point of operation at any time. Pullback devices automatically withdraw the operator's hands from the point of operation during the machine cycle. Robotics Safeguards Robotics safeguards include presence-sensing devices, barriers, interlocked barriers, perimeter guards, awareness barriers, or awareness signals.  Additional safeguards are needed when an operator must enter the work envelope to maintain or train the robot, such as lockout and tagout procedures, reduced operating speed, blocks or stops, emergency shutoff controls, and pendant control. Pendant Control Pendant control allows an operator to control a robot from within the work envelope at slow speed, with emergency stop capabilities. Zero Mechanical State (ZMS) ZMS recognizes that detailed procedures are necessary to ensure a machine or system is safe for maintenance, setup, or cleaning operations. Locking out the main power sources of a machine or system may not remove all sources of energy, and pneumatic, hydraulic, or other fluid lines or components may still be pressurized and need to be relieved or isolated to make them safe. Safeguarding Devices Presence-sensing devices, such as photoelectric, radio frequency, or electromagnetic devices, attach to the machine's control system to stop operation when the sensing field is disturbed. Presence-sensing mats detect a predetermined weight on the mat to stop the machine's operation. Point-of-Operation Safeguards Two-hand control requires concurrent and continued use of both hands to prevent them from entering the danger area. Two-hand trip requires concurrent use of both hands at the start of the machine cycle to prevent them from being in the danger area. Barrier Guards Type "A" Gate is a moveable barrier applicable to mechanical power presses, providing a barrier between the danger area and the operator until the completion of the machine cycle. Type "B" Gate is a moveable barrier applicable to mechanical power presses and press brakes, providing a barrier between the danger area and the operator during the downstroke. Awareness barriers alert people to a hazardous area or operation, and a warning should explain the machine's hazard and the purpose of the barrier. Hood guard is a circular table saws guard that "floats" vertically as material is moved into the blade. Adjustable and Self-Adjusting Guards  Adjustable guards are barriers that adjust for a variety of production operations, but may require frequent maintenance or adjustment and can be made ineffective by the operator. Self-adjusting guards move according to the size of the stock entering the point of operation, but do not provide maximum protection. Restraint and Pullback Devices Restraint devices connect the operator's wrists to a fixed anchor point, limiting their hands from reaching the point of operation at any time. Pullback devices automatically withdraw the operator's hands from the point of operation during the machine cycle. Robotics Safeguards Robotics safeguards include presence-sensing devices, barriers, interlocked barriers, perimeter guards, awareness barriers, or awareness signals. Additional safeguards are needed when an operator must enter the work envelope to maintain or train the robot, such as lockout and tagout procedures, reduced operating speed, blocks or stops, emergency shutoff controls, and pendant control. Pendant Control Pendant control allows an operator to control a robot from within the work envelope at slow speed, with emergency stop capabilities. Zero Mechanical State (ZMS) ZMS recognizes that detailed procedures are necessary to ensure a machine or system is safe for maintenance, setup, or cleaning operations. Locking out the main power sources of a machine or system may not remove all sources of energy, and pneumatic, hydraulic, or other fluid lines or components may still be pressurized and need to be relieved or isolated to make them safe. Safeguarding Devices Presence-sensing devices, such as photoelectric, radio frequency, or electromagnetic devices, attach to the machine's control system to stop operation when the sensing field is disturbed. Presence-sensing mats detect a predetermined weight on the mat to stop the machine's operation. Point-of-Operation Safeguards Two-hand control requires concurrent and continued use of both hands to prevent them from entering the danger area.  Two-hand trip requires concurrent use of both hands at the start of the machine cycle to prevent them from being in the danger area. Barrier Guards Type "A" Gate is a moveable barrier applicable to mechanical power presses, providing a barrier between the danger area and the operator until the completion of the machine cycle. Type "B" Gate is a moveable barrier applicable to mechanical power presses and press brakes, providing a barrier between the danger area and the operator during the downstroke. Awareness barriers alert people to a hazardous area or operation, and a warning should explain the machine's hazard and the purpose of the barrier. Hood guard is a circular table saws guard that "floats" vertically as material is moved into the blade. Adjustable and Self-Adjusting Guards Adjustable guards are barriers that adjust for a variety of production operations, but may require frequent maintenance or adjustment and can be made ineffective by the operator. Self-adjusting guards move according to the size of the stock entering the point of operation, but do not provide maximum protection. Restraint and Pullback Devices Restraint devices connect the operator's wrists to a fixed anchor point, limiting their hands from reaching the point of operation at any time. Pullback devices automatically withdraw the operator's hands from the point of operation during the machine cycle. Robotics Safeguards Robotics safeguards include presence-sensing devices, barriers, interlocked barriers, perimeter guards, awareness barriers, or awareness signals. Additional safeguards are needed when an operator must enter the work envelope to maintain or train the robot, such as lockout and tagout procedures, reduced operating speed, blocks or stops, emergency shutoff controls, and pendant control. Pendant Control Pendant control allows an operator to control a robot from within the work envelope at slow speed, with emergency stop capabilities. Zero Mechanical State (ZMS)  ZMS recognizes that detailed procedures are necessary to ensure a machine or system is safe for maintenance, setup, or cleaning operations. Locking out the main power sources of a machine or system may not remove all sources of energy, and pneumatic, hydraulic, or other fluid lines or components may still be pressurized and need to be relieved or isolated to make them safe. Hazard Control Hazard control involves eliminating or reducing the risk resulting from a hazard Two key components of hazard control are planning and designing, where planning involves developing a method for achieving something and designing is an extension of planning that incorporates more detailed and specific information Design Errors Design errors can introduce hazards, such as: o Failure to convert square inches to square feet, leading to a large error in a load calculation o Failure to include a factor of safety in a structural calculation o Using the wrong factor of safety o Failure to envision the use environment, such as wet or muddy floors Hazards in Production and Distribution Hazards can result from production and distribution activities, such as: o Replacing one chemical with another, introducing toxic or flammable hazards o Inadequate packaging, leading to a release of hazardous materials Hazards in Maintenance and Repair Hazards can arise from insufficient, delayed, or improper maintenance and repair, such as: o Failure to tighten a bolt or tightening it too much o Failure to lock out or provide lockout Communication Poor communication or failures in communication can introduce hazards Hazards can arise when changes in design, operations, and procedures are not communicated adequately to those impacted Principles of Hazard Control To minimize hazards, one must be able to: o Recognize them o Define and select preventive actions  o Assign responsibility for implementing preventive actions o Provide a means for measuring effectiveness Priorities Priorities for reducing hazards include: o Eliminate/replace the hazard o Reduce the hazard level o Provide safety devices o Provide warnings o Provide safety procedures and protective equipment Reducing the Hazard Reductions in the degree of severity lead to less injury, illness, or damage Strategies for reducing hazard severity include: o Placing hazards where there are few people o Using smaller quantities of flammable or toxic material o Reducing energy levels at an occupied location o Implementing a sprinkler system Reducing the probability of occurrence means that a hazard is less likely to result in an incident Strategies for reducing probability of occurrence include: o Designing for lower failure rates o Using redundancy o Avoiding single-point failures Redundancy-Backup System Providing redundancy in an operation or system can reduce the probability of error or failure Hazardous Locations Hazardous locations are classified into three categories: o I: Locations where flammable gases or vapors are present in quantities sufficient to produce explosive or ignitable mixtures o II: Locations hazardous because of the presence of combustible dust o III: Locations hazardous because of the presence of easily ignitable fibers or flyings Safety Precautions Using a rubber pad rated for electrical distribution line work can insulate the worker from other conductors  Defective or damaged cords can cause shocks, burns, or fires, and proper use and inspection of cords and wires are essential Hazard Control Hazard control involves eliminating or reducing risks resulting from hazards. Planning and design are critical in hazard control, as design errors can lead to failures and hazards. Failure to consider the use environment, making inadequate assumptions, and using wrong factors of safety can introduce hazards. Production and Distribution Hazards can arise from production and distribution activities, such as replacing one chemical with another or inadequate packaging. Insufficient, delayed, or improper maintenance and repair can also introduce hazards. Communication Poor communication can introduce hazards, especially when changes in design, operations, and procedures are not adequately communicated. The four components of communication are sender, message, media/channel, and decoding, receiver, and feedback. Principles of Hazard Control To minimize hazards, one must recognize them, define and select preventive actions, assign responsibility, and provide a means for measuring effectiveness. Historical data can help identify or anticipate hazards that may exist or potentially exist. Reduce the Hazard Priorities for reducing hazards are: Eliminate/replace the hazard Reduce the hazard level Provide safety devices Provide warnings Provide safety procedures and protective equipment Reductions in severity lead to less injury, illness, or damage. Examples of severity reduction include placing hazards where there are few people and using smaller quantities of flammable or toxic materials. Redundancy-Backup System Providing redundancy in an operation or system can reduce the probability of error or failure.  Examples include designing for lower failure rates, using redundancy, and avoiding single-point failures. Hazardous Locations Hazardous locations are classified into three categories: Class I: Flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures. Class II: Combustible dust is present. Class III: Easily ignitable fibers or flyings are present. Defective or Damaged Cords Improper use of cords can cause shocks, burns, or fires. Safety precautions include insulating live wires, inspecting cords and wires before use, and using only 3-wire type cords rated for hard or extra-hard usage. Accident Reconstruction The formula for calculating stopping distance is S = V2/30 μ, where S is distance, V is initial velocity, and μ is the coefficient of friction for tires on pavement. Railroads Hazards include explosions, fires, and releases of toxic materials. Most rail deaths and injuries result from grade crossing accidents with motor vehicles. Controls include barrier gates, sensors, and thermally insulated tank cars. Aviation Hazards Leaking fuel tanks and ignition can be disastrous. Icing of wings and loss of lift is still a danger in severe weather. Detecting and avoiding wind shear, particularly in clear weather, is a challenge. Controls include on-board computers and instruments for navigation, flight control, and management. Pinch Point Hazards Pinch point hazards occur when one or more objects move towards each other, crushing or shearing whatever comes between them. Examples include in-running nip points and self-propelled interlocks. Distance and Location  The minimum distance required from a floor or walking surface to mechanical power transmission apparatus varies with different standards, although 7 or 8 ft is often used. Enclosure Guards Fixed guards should be fixed to the machine to prevent additional hazards, such as pinch points. Most guards should permit viewing the point of operation. Limitations of enclosure guards include not being practical for changing production runs and requiring guard removal for machine adjustment and repair. Hazard Control Hazard control involves eliminating or reducing risks resulting from hazards. Planning and design are critical in hazard control, as design errors can lead to failures and hazards. Failure to consider the use environment, making inadequate assumptions, and using wrong factors of safety can introduce hazards. Production and Distribution Hazards can arise from production and distribution activities, such as replacing one chemical with another or inadequate packaging. Insufficient, delayed, or improper maintenance and repair can also introduce hazards. Communication Poor communication can introduce hazards, especially when changes in design, operations, and procedures are not adequately communicated. The four components of communication are sender, message, media/channel, and decoding, receiver, and feedback. Principles of Hazard Control To minimize hazards, one must recognize them, define and select preventive actions, assign responsibility, and provide a means for measuring effectiveness. Historical data can help identify or anticipate hazards that may exist or potentially exist. Reduce the Hazard Priorities for reducing hazards are: Eliminate/replace the hazard Reduce the hazard level Provide safety devices Provide warnings Provide safety procedures and protective equipment  Reductions in severity lead to less injury, illness, or damage. Examples of severity reduction include placing hazards where there are few people and using smaller quantities of flammable or toxic materials. Redundancy-Backup System Providing redundancy in an operation or system can reduce the probability of error or failure. Examples include designing for lower failure rates, using redundancy, and avoiding single-point failures. Hazardous Locations Hazardous locations are classified into three categories: Class I: Flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures. Class II: Combustible dust is present. Class III: Easily ignitable fibers or flyings are present. Defective or Damaged Cords Improper use of cords can cause shocks, burns, or fires. Safety precautions include insulating live wires, inspecting cords and wires before use, and using only 3-wire type cords rated for hard or extra-hard usage. Accident Reconstruction The formula for calculating stopping distance is S = V2/30 μ, where S is distance, V is initial velocity, and μ is the coefficient of friction for tires on pavement. Railroads Hazards include explosions, fires, and releases of toxic materials. Most rail deaths and injuries result from grade crossing accidents with motor vehicles. Controls include barrier gates, sensors, and thermally insulated tank cars. Aviation Hazards Leaking fuel tanks and ignition can be disastrous. Icing of wings and loss of lift is still a danger in severe weather. Detecting and avoiding wind shear, particularly in clear weather, is a challenge. Controls include on-board computers and instruments for navigation, flight control, and management. Pinch Point Hazards  Pinch point hazards occur when one or more objects move towards each other, crushing or shearing whatever comes between them. Examples include in-running nip points and self-propelled interlocks. Distance and Location The minimum distance required from a floor or walking surface to mechanical power transmission apparatus varies with different standards, although 7 or 8 ft is often used. Enclosure Guards Fixed guards should be fixed to the machine to prevent additional hazards, such as pinch points. Most guards should permit viewing the point of operation. Limitations of enclosure guards include not being practical for changing production runs and requiring guard removal for machine adjustment and repair. Hazard Control Hazard control involves eliminating or reducing risks resulting from hazards. Planning and design are critical in hazard control, as design errors can lead to failures and hazards. Failure to consider the use environment, making inadequate assumptions, and using wrong factors of safety can introduce hazards. Production and Distribution Hazards can arise from production and distribution activities, such as replacing one chemical with another or inadequate packaging. Insufficient, delayed, or improper maintenance and repair can also introduce hazards. Communication Poor communication can introduce hazards, especially when changes in design, operations, and procedures are not adequately communicated. The four components of communication are sender, message, media/channel, and decoding, receiver, and feedback. Principles of Hazard Control To minimize hazards, one must recognize them, define and select preventive actions, assign responsibility, and provide a means for measuring effectiveness. Historical data can help identify or anticipate hazards that may exist or potentially exist. Reduce the Hazard  Priorities for reducing hazards are: Eliminate/replace the hazard Reduce the hazard level Provide safety devices Provide warnings Provide safety procedures and protective equipment Reductions in severity lead to less injury, illness, or damage. Examples of severity reduction include placing hazards where there are few people and using smaller quantities of flammable or toxic materials. Redundancy-Backup System Providing redundancy in an operation or system can reduce the probability of error or failure. Examples include designing for lower failure rates, using redundancy, and avoiding single-point failures. Hazardous Locations Hazardous locations are classified into three categories: Class I: Flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures. Class II: Combustible dust is present. Class III: Easily ignitable fibers or flyings are present. Defective or Damaged Cords Improper use of cords can cause shocks, burns, or fires. Safety precautions include insulating live wires, inspecting cords and wires before use, and using only 3-wire type cords rated for hard or extra-hard usage. Accident Reconstruction The formula for calculating stopping distance is S = V2/30 μ, where S is distance, V is initial velocity, and μ is the coefficient of friction for tires on pavement. Railroads Hazards include explosions, fires, and releases of toxic materials. Most rail deaths and injuries result from grade crossing accidents with motor vehicles. Controls include barrier gates, sensors, and thermally insulated tank cars. Aviation Hazards Leaking fuel tanks and ignition can be disastrous. Icing of wings and loss of lift is still a danger in severe weather.  Detecting and avoiding wind shear, particularly in clear weather, is a challenge. Controls include on-board computers and instruments for navigation, flight control, and management. Pinch Point Hazards Pinch point hazards occur when one or more objects move towards each other, crushing or shearing whatever comes between them. Examples include in-running nip points and self-propelled interlocks. Distance and Location The minimum distance required from a floor or walking surface to mechanical power transmission apparatus varies with different standards, although 7 or 8 ft is often used. Enclosure Guards Fixed guards should be fixed to the machine to prevent additional hazards, such as pinch points. Most guards should permit viewing the point of operation. Limitations of enclosure guards include not being practical for changing production runs and requiring guard removal for machine adjustment and repair.