Ch 3. Concepts of Hazard Avoidance - PowerPoint Presentation

1. Ch 3. Concepts of Hazard Avoidance

2. ContentsThe Enforcement ApproachThe Psychological ApproachThe Engineering ApproachThe Analytical ApproachHazard-Classification Scale

3. The enforcement ApproachThis approach is based on behavioral modification by punishment “Since people neither assess hazards properly nor take prudent precautions, they should be given rules to follow and be subject to penalties for breaking those rules”OSHA has forced thousands of industries to comply with regulations that have changed workplaces and made millions of jobs safer and more healthful.It is difficult to see any general improvement in injury and illness statistics as a result of enforcement.Although some categories, such as trenching and excavation cave-ins, have shown marked improvement.

4. weaknesses of the enforcement approachMandatory language employing the words ‘always’ and ‘never’ is really inappropriate when dealing with the uncertainties of safety and health hazards. How about adding exceptions??Need to consider countless of possibilities!Can alleviate the problemSee case study 3.2 in textbook

5. weaknesses of the enforcement approachPeople will find a way around the lawVery expensive to monitor and enforce

6. weaknesses of the enforcement approachSometimes a fine is a negative and inappropriate response in a vain attempt to place blame after the fact when an accident has occurred. Overall, the enforcement approach leads to problems when it is the only response to dealing with a safety or health hazardExample: mandatory helmet law for motorcycle ridersPure enforcement vs. convincing (ex. Statistics that helmets save lives)

7. The Psychological ApproachThis approach attempts to reward safe behaviorsThe familiar elements of the psychological approach are posters and signs reminding employees to work safely.Signs:

8. The Psychological ApproachPosters

9. The Psychological ApproachThe psychological approach is very sensitive to the support of top management.If such support is absent, the approach is very vulnerableExample: a rule requiring safety glasses to be worn in the production area is undermined when top management does not wear safety glasses when visiting the production floor.New young workers, are particularly influenced by the psychological approach to safe and health.acquisition of behavior by modeling (or social learning): New workers follow the behavior of older workersAccident reports confirm that a larger percentage of injuries are caused by unsafe acts by workersThis fact emphasizes the importance of the psychological approach in developing good worker attitudes toward safety and health.

10. The Engineering ApproachRatio 88:10:2 (Heinrich, 1959)Unsafe acts (88%): Unsafe condition (10%): Unsafe causes (2%)Recently, Heinrich’s ratio has been questioned:The current trend is to give increase emphasis to the workplace machinery, environment, guards, and protection systems (i.e., the conditions of the workplace).For incidents that at first appear to be caused by “worker carelessness”: could they have been prevented by a process redesign??

11. The Engineering ApproachExample: A worker has to take 10-15 minutes to wear the correct P.P.E. to enter an area to turn off a control switch which only took 10 seconds. What could go wrong? From human behavior aspect, the worker could take a shortcut and not wear PPE  risk of injury or illnessPossible engineering approach solution: Redesign the process and replace the control switch outside the restricted area.

12. The Engineering ApproachLines of defense against health hazards

13. The Engineering ApproachExample: the problem of chronic exposure to noise that can damage the workers’ hearingThe first and preferable line of defense (engineering controls) would be finding some way to eliminate the source of the noise exposureAn administrative or work-practice control would be to schedule employees on a rotation basisThe last resort should be personal protective equipment or hearing protectors

14. The Engineering ApproachEngineering controls deal directly with the hazard by removing it, ventilating it, suppressing it, or otherwise rendering the workplace safe and healthful.

15. The Engineering ApproachSafety factor: consider a margins for variationExamples: The safety factor for the design of scaffold components is 4:1The safety factor for the design of overhead crane hoists is 5:1The safety factor for the design of scaffold ropes is 6:1 Scaffold ropes are designed to withstand six times the intended loadSelection of safety factors must be reasonable, feasible and based on the evaluation or classification of degree of hazardCost, weight, supporting structure, speed, horsepower, and size are all factors that may be affected by selecting too large a safety factor

16. The Engineering ApproachFail-Safe principlesAdditional principles of engineering design that consider the consequences of component failure within the system. These principle labeled here as fail-safe principles, and there are identified:General fail-safe principleFail-safe principle of redundancyPrinciple of worst caseGeneral fail-safe principleA failure within the system will result in a safe mode

17. The Engineering ApproachGeneral Fail-Safe PrincipleAny other examples??

18. The Engineering ApproachFail-safe principle of redundancyA critically important function of a system, subsystem, or components can be preserved by alternate parallel of standby unitsRedundancy principle has been widely used in the aerospace industry.

19. The Engineering ApproachPrinciple of worst caseThe design of a system should consider the worst situation to which it may be subjected in use.A recognition of Murphy’s law “If anything can go wrong, it will”Example 1: an explosion-proof motors in ventilation system  for rooms in which flammable liquids are handledExample 2: the concept of defensive driving

20. The Engineering ApproachPrinciple of worst caseExplosionproof motors are much more expensive than ordinary motors, and industries may resist the requirement to install them.Consider the following scenario in a processes in which the vapor levels of the substances mixed never even get close to the explosive rangeIn a hot summer day on which spill happens to occur.The hot weather raises the vapor level of the flammable liquid being handled.A spill at such an unfortunate time dramatically increases the liquid surface exposure, which makes the problem many time worse.

21. The Engineering ApproachDesign principlesEliminate the process or cause of the hazard.It is the duty of safety and health professionals to question old and accepted ways of doing things if these ways are hazardous.Substitute an alternate process or materials.Reduce or slow down exposure to hazardous processes or materials.Guard personnel from exposure to the hazard.A process is absolutely essential and there is no substitute for it.Install barriers to keep personnel out of the area.Warn personnel with visible or audible alarms.Use warning labels to caution personnel to avoid the hazard.Use filters to remove exposure to hazardous effluents.Design exhaust ventilation systems to deal with process effluents.Consider the human interface.

22. The Engineering ApproachPitfallsCertain unusual circumstances can make the engineering solution inappropriate or even unsafe. Workers remove or defeat the purpose of engineering controls or safety devices.Examples: over-speed alarm sound; the removal of guards from machinesIf engineered system does not do the job for which it was intended, it can do more harm than good by creating a false sense of security. Examples: use of shoulder lane in highway; the hoist limit switch on an overhead crane.

23. The Analytical ApproachThe analytical approach deals with hazards by studying their mechanisms, analyzing statistical histories, computing probability of accidents, conducting epidemiological and toxicological studies, andweighing costs and benefits of hazard elimination.Accident AnalysisFailure Modes and Effects Analysis (FMEA)To trace the effect of individual component failures on the overall, or catastrophic, failure of equipment.Fault-Tree AnalysisLoss Incident Causation ModelsCost-Benefit Analysis Fishbone Diagrams and Swiss Cheese TheoryToxicology and Epidemiological study

24. Failure Modes and Effects AnalysisInductive reasoning - Bottom-up technique (different from FTA)Performed by answering a series of questions like:What can fail?How does it fail?How frequently will it fail?What are the effects of the failure?What is the reliability/safety consequence of the failure?ID #ComponentFailure modeFailure causeFailure effectSeverityOccurrenceDetectabilityRPNRecommendations

25. Failure Modes and Effects AnalysisRisk Priority Number (RPN) = a combination of severity, occurrence (freq.), and detection. (Raytheon method below…)Severity: Scale 1-10, 1=no impact, 10=catastrophic impact/hazardousOccurrence: Scale 1-10, 1=predicted <3 defects/million, 10=>500K defects/million Detectability: Scale 1-10, 1=always detected by current control plan, 10=unable to detect

26. Failure Modes and Effects Analysis

27. Failure Modes and Effects Analysis (ANGLE GRINDER ) exampleIDComponent Failure modeFailure causeFailure effectSeverityOccurrenceDetectabilityRPNRecommendation1SwitchStay on- Defect.- Worker forgets to switch it off .- Disc breakage and Severe injury. 8  2  7  112  - Routine maintenance.- Add safety sensor to turn switch off when unplugged.2Disc Diamond disc breakage . -Using wrong disc- Too much speed-Severe Injury864192-Refer to manufacturer user guide and recommendations

28. Fault-Tree AnalysisFault trees are graphical models using logic gates and fault events to model the cause–effect relationships involved in causing the undesired eventDeductive reasoningStarts with general and moves toward specificRequires knowing the “top event” or end point in advanceGeneral rules:Moving down the tree reveals causesMoving up the tree reveals effectsNo gate-to-gate connectionsDo not draw lines from two gates to single input

29. Fault-Tree AnalysisAND gate – all inputs to gate requiredOR gate – any input to gate is sufficientBasic eventEvent

30. AND gateOR gateOxygen, ignition heat, and fuel must be existed at the same time to happen fire.Open flame or static spark can be ignition heat.Fault-Tree Analysis

31. Fault-Tree Analysis (Example)Amputate finger with table sawFinger contacts bladeBlade is rotatingNo guard in placePoorly designed guardSaw plugged inE-stop not pushedSwitch toggled on

32. AccidentABCDEAND gates: B and DOR gates: A, C and E (Accident)How to calculate the probability of the accidentFault-Tree Analysis

33. AND gate represents a combination of independent events. That is, the probability of any input event to an AND gate is unaffected by any other input event to the same gate. In set theoretic terms, this is equivalent to the intersection of the input event sets, and the probability of the AND gate output is given by: P (A and B) = P (A ∩ B) = P(A) P(B) OR gate, on the other hand, corresponds to set union: if the two event are dependent, P (A or B) = P (A ∪ B) = P(A) + P(B) - P (A ∩ B) If two events are mutually exclusive, P (A or B) = P (A ∪ B) = P(A) + P(B) Since failure probabilities on fault trees tend to be small (less than .01), P (A ∩ B) usually becomes a very small error term, and the output of an OR gate may be conservatively approximated by using an assumption that the inputs are mutually exclusive events: P (A or B) ≈ P(A) + P(B), P (A ∩ B) ≈ 0Fault-Tree Analysis

34. P(A)P(B)P (A and B) = P (A ∩ B) = P(A) P(B) AND gate:OR gate:P (A or B) = P (A ∪ B) = P(A) + P(B) - P (A ∩ B)  DependentP (A or B) = P (A ∪ B) = P(A) + P(B)  Mutually exclusiveFault-Tree Analysis

35. Fault-Tree Analysis – the probabilities of accident occurrence

36. Fault-Tree AnalysisExample - Dependent

37. Fault-Tree AnalysisExample - mutually exclusiveProbability of FIRE = 0.21 * 1 * 0.35 = 0.0735

38. Boolean algebra simplificationa.a=aa+a=aa+a.b=aa.(a+b)=aMinimum Cut sets – minimum sequence that can cause top eventFault-Tree Analysis

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41. Loss Incident Causation ModelsMcClay’s Model (Universal model of causation)Proximal cause: a direct hazard in the conventional senseExample, a missing guard on a punch press.Distal cause: management attitude or policy that is deficient in allocating resources and attention to the elimination of hazardsDistal causes are as important as proximal causes, because distal causes create and shape proximal causesPoint of irreversibility:Despite the number and variety of proximal causes, only a few select cases will result in a sequence of events in which the point of irreversibility is reachedOnce this point is reached, a loss incident is unavoidable.

42. Loss Incident Causation Models

43. Loss Incident Causation ModelsFigure 3.8: A universal model for the occurrence of loss incidentsThe relationship between distal and proximal causesSphere of controlPoint of irreversibility

44. The Analytical ApproachCost-Benefit AnalysisBenefit to safety and health consists ofHazard reductionSome quantitative assessment of hazard must be made  But such probabilities of injury or illness are very difficult to determineAn estimate of expected risk after the improvementHowever, it is very difficult to make the estimation of the benefit side of the picture.

45. The Analytical ApproachPROBLEM: Employees were required to use a jack hammer to remove and break up air set core from castings. Stressors included vibration & bending over for 4-8 hrs/day.SOLUTION: A core lump crusher has been purchased to eliminate the use of the jack hammer. COST: $51,000COST RECOVERY TIME: 8-12 monthsBENEFITS: Eliminated strain from repetition, vibration and poor posture, increased productivity, recovery rate and reduced manpower.BEFOREAFTER

46. Cost-Benefit Analysis

47. Cost-Benefit Analysis (Example)Consider a chemical plant with a process that if it were to explode could lead to:30 fatalities, 50 permanently injured, 90 seriously injured, 300 slightly injuredThe rate of this explosion happening has been analyzed to be about 1 x 10^-5 per year, which is 1 in 100,000 per year. The plant has an estimated lifetime of 25 years.Based on the severity of the consequences of such explosions  a disproportion factor (DF) of 10 was suggested by the safety manager

48. Cost-Benefit Analysis (Example)What is disproportion factor (DF)? A factor representing the magnitude of the consequences and the frequency of realizing those consequencesThe greater the risk, the greater the DFIn the example, the DF (10) reflect the consequences of an explosions which are high.

49. Cost-Benefit Analysis (Example)The cash valuations of preventing safety effects on people are presented in the table:Hypothetically, how much could the company reasonably spend to eliminate (reduce to zero) the risk from the explosion??CaseCost $FATALITY$1,336,800Permanent injury$207,2000Serious injury $20,500Slight injury$300

50. Cost-Benefit Analysis (Example)Answer: If the risk of explosion were to be eliminated the benefits can be assessed to be:Fatalities: 30 * 1336800 * 1*10^-5 * 25 yrs = $10026Permanent injuries: 50 * 207200 * 1*10^-5 * 25 yrs = $2590Serious injuries: 90 * 20500 * 1*10^-5 * 25 yrs = $461.25Slight Injuries: 300 * 300 * 1*10^-5 * 25 yrs = $22.5Total benefits = $13099.75Therefore, it might be reasonably practicable to spend up to somewhere in the region of $130997.5 ($13099.75x 10) to eliminate the risk of an explosion.Amount above that can be considered grossly disproportionate to the benefits.

51. Fishbone Diagram

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53. Swiss Cheese TheoryInadequate guard designImproper installationIncomplete worker trainingSupervision laxAccidents occur when protective measures are left to chance.The Swiss cheese holes may line up.

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55. Hazard-Classification ScaleFour categories of hazards or standards violations by OSHAImminent dangerSerious violationsNon-serious violationsDe minimis violationsThe 10 points scale (Table 3.1). (Refer to textbook for full table) Subjective description of 10 levels of hazards10: the worst hazard imaginable; …………..; 1: the mildest hazardThe scale is not related to cost

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57. Comparison of OSHA classification and 10-point scale

58. The Risk Assessment Code (RAC) system

59. The Risk Assessment Code (RAC) system4 levels of mishap severity and 4 levels of mishap probability (Table 3.2)

60. British Standard Hazard ClassificationStandard Code of Practice for Safety of Machinery (A British Standard)

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