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Date Created: 10/15/15
OSH 452 Topic Network Theory 1 Definitions Reliability Network To get desired output you must have certain inputs Accident Network To get undesired output accident certain inputs must exist AAA A Accldont 2 Series System Reliability Example AA Battery P Starter 8 Succussful Motor Motor P 399 Turnover PSuccess PA and B the only way C can happen is ifA and B happens Series system is not desirable because system reliability is lower than component reliabilities Accident Example Accident C can only happen ifA happens and then B happens Both events must occur or A must fail to work and a must fail to work before 9 accident occurs Am I Electrical F n wmatiG Unsuccessful Starting Starting start System System Accident P 1 P 3 A series relationship is good because the probability of an accident decreases 3 Parallel System Fire 1 Destruction Acctdent Example of Boiler Explosion 3 Overall probability of destruction is higher than individual probability of failure A parallel relationship in accident systems is BAD because the probability ofan accident increases v Gen1works Gen2works 9 8 72 v Gen1works Gen2fails 9 2 18 v Gen1fails Gen2works 1 8 08 Top39c OSH 452 Boolean Algebra Basic Boolean Principles 1 Universe Everything you are interested in Represented by Rectangle Symbol w Set or Group Group of events which have a characteristic in Common Compliment Everything not in common with set Pronounced not A Mutually exclusive Can39t be in both sets lntersectionThe probability of an event belonging to both groups Symbol is n PA n B Pronounced A intersect B PA n B PA PB GB 6 Union Either oftwo groups being considered satis es the criteria Symbol is U PA U B Pronounced A union B 7 Independence One group has no effect on the other Occurrence in A has no in uence on B 8 Dependence One event has an effect on the other Expansion of Boolean Principles 9 There is a unique relationship ofthe universe to any group The following equations are always true PM U R 1 The probability ofa union between the universe and a group is always 1 PM 0 R PR The probability of an intersection between the universe and any group is the probability of that group A Smoking gt 2 packs a day 2 B Women 20 29 years old 25 C Women 30 39 years old 3 PB u a PM n B Pmuq chm HBUQUHM A Smoking gt 2 packs a day 2 B Women 20 29 years old 25 C Women 30 39 years old 3 D Infants lt1 years old 01 E Teenagers 1519 years old 03 PA n E 002 PD39U E39 PD39 n E39 VI 9 I PB U E 0 PA OSH 452 Topic Cut Sets Reliability system 6 quotl Cutting the system What blocks must fail at the same time in order to make the system fail Minimum Cut Sets All blocks in a set are necessary for failure Provides the upper bound on the probability of system failure Calculation OSH 452 Tog39c Fault Tree Analysis Construction 1 Developed by 2 Uses of Fault Tree Analysis 3 Timing 4 Scope of Fault Tree Analysis Construction Approach 5 Overall construction sequence A Identify undesired event B Determine all events leading to undesired event C Determine critical paths cut sets D Quantify end events E Determine the importancesignificance ofvarious paths 6 Types of Fault Events A Fault the failure ofa component ofa system B Primary fault Failure of component due to internal characteristics in normal operating conditions C Secondary fault Failure due to external stresses or environment D Commanded fault Failure due to incorrect input to the component quotNo Miracle Rulequot Symbols A Fault Eventwhich must be further analyzed primarycommand fault rectangle B Basic Eventno further analysis necessary secondary fault circle Basic Event C Undeveloped Event not analyzed further due to lack of information or is insigni cant diamond D Normal event Event that is expected to occur normally E Gates 1 quotorquot gate one or more events apply m 2 quotandquot gate all events apply Examples Car skidding on an icy road Slippery Pavement Excess Speed 9 Characteristics of Fault Tree Analysis A Deductive approach B Focuses on the undesired event C Not restricted to series amp parallel networks D Allows for either quantitative and qualitative analysis E Forces quotsystem insightquot F Negative Very tedious and a costly approach OSH 452 Togic Fault Tree Analysis Quantification 1 Quanti cation of Fault Trees B CutSetdevelopment 1 Logicalgates a quotorquot any ofthe events could have caused the undesired event Boolean quotunionquot or HqPmm b quotandquot intersection or HqPmm A Steps Do in listed order 1 Start at top of tree amp develop equations 1 level at a time 2 Substitute events into the overall equation 3 Reduce the equation using Boolean algebra 4 Determine most critical paths 5 Determine equivalent fault tree 6 Relative determination of safety 1 Quantify the fault tree ALC CBJK ALBJK Draw equivalent tree Handout Calculate probability 1 m Nun 10 Inninnn slmwllllmllun Figure out equation KBC B D Simplify equation Multiply B by BD and C by BD KBBBDB CD Factor BB is same as B KBBDBCCD Continue to Factor B is in BD and BC remove them K B CD Solve Probability substitute numbers K 0015 0004 0002 converted powers to decimals K 0015 00000008 K 00150008 or 150008 x10 3 OSH 452 Top39c Fault Tree Analysis Wrapup 1 Other quantitative measures A Fault Rate Probability of failure over a speci ed time interval k B Unreliability Probability of one failure over a specified time interval R C Mean Down Time Mean time system is in a fault state D Expected Faults Number oftimes the fault is expected in a given time interval 2 Summary of Fault Tree A Deductive approach amp analyzes interrelationships and common faults B Requires detailed design information amp is done at a later period during the system life cycle C Limitations 1 Symbols confusing 2 Gives cause and effect information only 3 Boolean algebra amp reductions may be tedious 4 Relatively costly Boiler Explosion Examples of how fault tree works Boiler Explosion Original Design Modify design by adding a warning device Boiler Explosion Pressure Relief Valve Fail Shut OSH 452 Togic Process Safety 1 History ofthe Standard A A 30year review ofthe chemical industry 100 largest loss events B Catastrophic events 1 Union Carbide 2 Phillips 66 C EPA Study D Clean Air Act Amendments CAAA of 1990 Title Process safety management of highly hazardous chemicals 2 Purpose Enhance awareness of safe handling amp storage of highly hazardous chemicals in industry 3 Applicability A Performancebased approach B Applies mainly to chemical oil paper food processing fabricated metals production companies and pyrotechnics amp explosives manufacturers C Covers plants that deal with speci c chemicals 330 in quantities above specified thresholds or that handle ammable liquids amp gases in quantities greater than 10000 lbs 4 Review of Major Components A Collect amp document data on process chemicals technology and equipment B Develop written operating procedures 1 Written procedures for all aspects of operation 1 Initial startup 2 Normal operations 3 Temporary operations 4 Emergency shutdown 5 Startup following normal shutdown 6 Steps for operating limits 7 Safety amp health considerations 8 Safety systems amp their function 2 3 4 5 6 Operating procedures must be readily accessible Procedures must reflect uptodate practices Must certify annually that operating procedures are current amp accurate Safe work practices must be implemented to ensure hazard control during operations Procedure changes must be properly authorized and updated amp affected employees trained C Establish a managementof change procedure D Employee participation E Conduct a prestartup review for new facilities F Train employees involved in the process G Evaluate contractors H Develop a mechanical integrity program Develop provisions for hot work permits J Emergency planning amp response K Conduct a compliance audit at least every three yearsto ensure that procedures and practices are adequate L lncident investigation M Conduct a process hazards analysis Must address 1 2 8 6 Process Flow Diagram Block Flow Diagram Process hazards Identification of previous incidents Engineering amp administrative controls used Human factors Consequences of failure of controls Strongly recommends block flow diagrams and process flow diagrams Euxmpll u pmquot Flaw nun 5 Analysis Techniques A Whatif Summary Pro ce dure Advantages Concerns B Checklists Summary Pro ce dure Advantages Concerns Provides comprehensive coverage of a broad range of hazards Brainstorming method whereby the applied experience ofthe team is used to derive potential operating problems and determine their effects ls relatively easy to use and good for relatively uncomplicated processes Quality depends on the reviewer39s experience amp background The right questions must be asked to perform an effective analysis Uses checklist previous developed Go down the checklist checking and answering questions posed Directly addresses the most important areas Checklist may miss important areas C Failure mode and effects analysis FMEA Summary Methodical approach to failure mode and consequences Procedure Each system component or subsystem is postulated to fail and the failure39s effect on the system and any external effects are determined Advantages Works best when studying a speci c item of equipment It39s semi quantitative approach assists in ranking hazards Concerns It assumes normal operation is satisfactory An accurate model or diagram must be developed to proceed effectively D Hazard and Operability Study HAZOP Summary Structured engineering review to determine the response of systems to deviations from design parameters Pro ce dure Process broken down into linevesselequipmentcontro operating sequence Node Guide words coupled to design parameters Deviation combination ofa guide word and a parameter Advantages Determines how deviations from design intentions can occur amp whether consequences of such deviations are hazardous Promotes employee involvement Concerns Its assumption that all designs are correct for normal situations Requires a good team leader and good model diagrams Timeconsuming and expensive E Fault tree analysis FTA Summary De nes various routes to a top event and quanti es probability of reaching that event Procedure Determine undesired events and causes that contribute to the events Advantages Provides objective information for decisionmaking Concerns Focuses on events rather than the process amp requires quantitative techniques amp expertise Often reserved for critical hazard situations F An appropriate equivalent methodology 6 Mandatory amp nonmandatory sections Process Safety Management Chemical Accidental Release Prev Trade secrets p Not covered 8 Positive effects A Reduce potential for a catastrophic incident B Reduce waste C Increase production and improve procedures OSH 452 Top39c Product Liability 1 Introduction 2 History 3 De nitions A Express warranty Statement by a manufacturer or dealer in writing or orally that the product will perform in a speci c way is suitable for a speci c purpose or contains specific safeguards B Implied warranty Implication by a manufacturer or dealer that a product is suitable for a speci c purpose or use or is in good condition or is safe by placing it on sale C Negligence Failure to exercise a reasonable amount of care or to carry out a legal duty so that injury or property damage occurs to another D Liability An obligation to rectify or recompense any injury or damage for which the liable person has been held responsible or for failure ofa product to meet a warranty E Strict Liability Concept that a manufacturer of a product is liable for injury due to a defect without necessity for a plaintiffto show negligence or fault E Care a High care that a very prudent and cautious person would undertake for the safety of others b Reasonable care exercised by a prudent man in observance ofhis legal duties toward others 0 Slight care less than that which a prudent man would exercise Foreseeability for safe design Manufacturer must be reasonable careful in designing and producing a product to avoid injuring others by exposing them to possible dangers Where hazards cannot be eliminated he is obligated to warn any prospective user of inherent dangers or properties ofthe product Product Liability Definitions Express warranty Statement by a manufacturer or dealer in writing or orally that the product will perform in a speci c way is suitable for a speci c purpose or contains speci c safeguards Implied warranty Implication by a manufacturer or dealer that a product is suitable for a speci c purpose or use or is in good condition or is safe by placing it on sale Negligence Failure to exercise a reasonable amount of care or to carry out a legal duty so that injury or property damage occurs to another Liability An obligation to rectify or recompense any injury or damage for which the liable person has been held responsible or for failure of a product to meet a warranty Strict Liability Concept that a manufacturer of a product is liable for injury due to a defect without necessity for a plaintiff to show negligence or fault Care Degree of care a High care that a very prudent and cautious person would undertake for the safety of others b Reasonable care exercised by a prudent man in observance ofhis legal duties toward others 0 Slight care less than that which a prudent man would exercise Privity lndicates a direct relationship between two persons or parties such as between a seller and buyer Foreseeability for safe design Manufacturer must be reasonable careful in designing and producing a product to avoid injuring others by exposing them to possible dangers Where hazards cannot be eliminated he is obligated to warn any prospective user of inherent dangers or properties of the product OSH 452 Tog39c Malfunctions 1 Introduction 2 Types of malfunctions 3 Causes of malfunctions 4 Minimizing Failures amp Hazards F FailSafe Design 1 Fail Operational 2 Fail Passive 3 Fail Active G Aspects of Monitoring Measuring a particular function Types of MonitorsWarning Devices A Visual B Auditory C Olfactory D Tactile Damage MinimizationContainment A Isolation keep damage contained C Minor Loss Acceptance acceptance ofa small loss to avoid a larger loss D Escape amp Survival Reduce damage to humans OSH 452 Top39c Introduction Hazard Analysis TechniquesMHA 1 Introduction to Hazard Analysis A Overall Goals a Better understand safety aspects of system b Provide project manager test planners etc data for tradeoff decisions 0 Demonstrate compliance with standard or objective B Key elements a Identi cation b Evaluation 0 Communication C Types ofAnalysis 1 General Types 2 Specialized Applications Sneak circuit analysis Software analysis Maintenance Hazard Analysis MHA Examination of each type of maintenance activity to determine if a hazard exists from its performance A Purpose Identify hazards to personnel and equipment that may be encountered or could result in improper maintenance B Examine all the systems operations and the interfacing of personnel in maintenance activities C Performed priorto the rst design review and is maintained current with the system designmodi cation D Data sources a Maintenance engineering analysis b Maintenance support plans and procedures 0 Maintainability data d Maintenance equipment amp maintenance facility drawings Top39c OSH 452 Preliminary Hazard Analysis 1 Preliminam Hazard Analysis A Purpose amp timing 1 Initial safety analysis done on system 2 Anticipate major hazard aspects of system 3 Basis to formulate 88 program tasks and criteria 4 Most effective in early conceptual development Input data required 1 Design sketches and information on alternate approaches 2 Functional flow diagrams 3 Safety experience of previous systems a b C d Lessons learned Nearmiss information Review of standardscodes Previous hazard analysis Scope 1 Identify possible hazardous components 2 ID possible hazardous operation 3 ID needed safety equipment and training 4 ID need for additional analysis Approach 1 Unstructured 2 Generic hazards 3 Models and mockups and computer models 4 Experience and creativity of analysts important Output Data 1 Narrative summary 2 PHA matrix F Example Analysis see Roland page 209 for form Hot water heatin 3 Stem SUBSYSTEM OPERATING FAILURE MODE ESTIMATED HAZARD HAZARD SEVERITY CONTROL PART MODE PROBABILITY DESCRIPTION EFFECTS REMARKS Under Steam pipe Occasional Release of Serious Critical 1 Evaluate design Heater Pressure failure at less Class C pressurized injury to CAT II standards for than design steam in an nearby pipes and j ints pressure occupied person 2 Test criteria area Analysis of proximity to nccun39i ed space Heated All Ignition of Remote Explosion System loss Catastrophic 1 Isolation of Space heated fuel Class D an CAT I fuel tank from bldg from broken fatalities building fuel line 2 Verification of pipe and joints Boiler Pressurized Failure due to Occasional Violent Facility Catastrophic Automate control High overpressure Class C rupture of damaged amp CAT I system 1 Operator boiler fatalities error 2 Regulator Occasional Violent Facility Catastrophic l Analyze failure Class C rupture of damaged amp CAT I pressure boiler fatalities regulation system 2 C of pressure relief valve 3 Feedwater Occasional Violent Facility Catastrophic 1 Backup supply system Class C rupture of damaged amp CAT I feedwater boiler fatalities 2 Automatic fuel shut off 3 Specify boiler design for minimum rupture hazard OSH 452 Top39c FHA 1 Fault Hazard Analysis A Uses 1 Veri cation that system meets designated criteria 2 Identi cation 3 Organize safety data B Input data required 1 Design speci cations and drawings 2 Speci cations of operational test environments 3 Interface control drawings 4 Description of handling maintenance and service equipment 5 Results of previous analysis C Scope total system Criteria No single failure or error will result in system loss or serious personnel injury D Approach 1 Divide system into its subsystems and components Example components a Mechanical device b Electrical devices c Chemical systems d Electrical wiring e Safety devices 2 Determine component failure modes which can potentially result in a hazard 3 Determine effects on subsystem and then system Flow Chart DHdSt 1 C1 quot39 quotquot Failure Mode 39 Eileen 1 E E E Output Data 1 Matrix sheets 2 Summary of hazards and controls needed N Analysis of Trident Nuclear Submarine propulsion system Pressure Tank System 1m 271 Flull mum analysis lam r luan unmr 7 u u r4 n quotmy mmmm mm M Ilur m nun Rrrv valx 1 we run mm mm Mum mmx ran an area Imam t nlummv mu LV tmuvml 1 mm W um I39muurr nmnn Mush my ulmm m Ivinlnrm vnmm mm W Impvbdlu 5mmquot um mun Wm WM pm Faixblww Hum twmlnn Hm Yam rpm m 1 m l my hnuucyd mm r warv Lam mm 13ml rum n N 39MIIJi lD X unit Jkptm mama mums uupmmbk mum mum My OSH 452 Top39c OHA amp FMEA 1 Hazard analysis previoust discussed A PHA B FHA 2 Operating Hazard Analysis OHA A Output Hazards resulting from tasks during operation maintenance accidents and post accident problems etc B Data Required 1 Speci c engineering speci cations and drawings 2 Information about support facilities 3 Detailed operating and maintenance procedures C Approach unstructured similar to PHA with matrix changed to re ect operating event task 3 Failure mode amp effects analysis FMEA A Output 1 Mechanical failure modes 2 Identify probability of failure B Data required 1 Detailed system specifications and operating conditions 2 Component failure rates C Approach 1 Identi es all failure modes 2 Uses FHA format 3 Identi es safety impact of failures 4 Example of FMEA Graphic of sprinkler system ITEM DESCRIPTION ITEM DESCRIPTION 1 Ball Drip 8 Tee Cannacuun 2 re Depanmam Connection 9 Main Drain Valve 3 Check Valve 10 Main Drain Flaw Test Line 4 Electric Alarm Ball 11 Check V 5 Water Flaw Indiranor 12 Hiserrom Main Water SuppIy 6 Tea Connection 1 Main Water Commt VaJva 7 Water Gauge Wet pipe sprinkler system typical riser with water indicator OSH 452 Top39c Probability Concept of probability Probability ratio of occurrences of speci ed types to total number of occurrences Probability Examples Be careful about the amount of data you have you must have enough data The last 10 years Acme taxi had the following experience 2002 2 1600 TOTAL 59 13125 You must be careful not to bias the probability when you choose which data to use Try to use as much data as possible Generally 35 years of data are suf cient PROBABILITY LIMITATIONS Probability is always bound by O and 1 ADDITION LAW PA or B PA PB MULTIPLICATION LAW PA and B PA PB COMPLEMENTARY LAW PNot A 1PA Given Information Accidents 0 or 1 or 2 or 3 or or 400 P0 1 2 3400 349 387 172 081 000 1 The numbers represent the probability that a company would experience that exact number of accidents in 400 trips In this example we assume that once an accident occurs the trip is over Therefore in 400 trips there can be only 400 accidents The total of all the probabilities of accidents the company might experience must equal 1 DEPENDENCE VS INDEPENDENCE Dependence What happens on one trial affects the probability of the next trial Independence What happens on one trial does not affect the probability ofthe next trial
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