Human Error & Risk Factor Affecting Reliability & Safety

SEMINAR

ON

“HUMAN ELEMENT FACTOR AFFECTING RELIABLITY & SAFETY-Treating Human errors

and risk factors in probabilistic analysis”

BY

DUSHYANT KALCHURI

M.TECH(PRODUCTION ENGG.)

DEPARTMENT OF

MECHANICAL ENGINEERING

CONTENTS :• Introduction• Faulty measures undertaken during the handling of equipment

And Unsafe Acts• Case Study On:

Computer System Interruptions By Human Errors

Utility Distributions Interruptions By Human Errors• Classification of Human Error according to system orientation• Human Reliability analysis• Technique for Human Error Rate Prediction• Error Prevention / Remediation• Accident Injury Sequence Model• Safety analysis• References

INTRODUCTION:• Many system reliability predictive methods are based

solely on equipment failures, neglecting the human component of man–machine systems (MMS).

• The reliability and safety of industrial and commercial power systems and processes (i.e., MMS) are dependent upon human characteristics and many dependent and dynamic interactive factors .

• The consequences of human errors are very diverse and can range from damage to equipment and property, injury to personnel or fatalities, to disruption of scheduled system operation, all of which represent a significant cost to society.

HUMAN ERROR:

• A failure on the part of the human to perform a prescribed act or task within specified limits of accuracy, sequence, or time, which could result in damage to equipment and property and disruption of scheduled operations or have no consequences at all.

• “ most of the human errors occur because humans are capable of doing so many different things in many diverse ways.”

• Generally 20%–50% of all equipment failures are due to human errors.

WHY A HUMAN PERFORMANCE IMPROVEMENT APPROACH??

80% Human Error 30% Individual

20% Equipment Failures

Human Error

Unwanted Outcomes70% Latent Organization Weaknesses

INDUSTRY EVENT CAUSESDUE TO HUMAN PERFORMANCE/ERROR

Source: INPO, Event Database, March 2000. For all events during 1998 and 1999.

215

26 3988

192

654

9 20

160

82

806

73118

0

100

200

300

400

500

600

700

800

900

Num

be

r o

f C

ause

s

1,676 = Org behavior (68%)

806 = Individual behavior (32%)

TAXONOMY OF HUMAN ERROR:

Interpretation

Situation Assessment

Plan

Intention ofAction

Action Execution

StimulusEvidence

Memory

MISTAKES SLIPS

LAPSES &MODE ERRORS

Knowledge Rule

TAXONOMY OF HUMAN ERROR MISAKES:

• Mistakes – failure to come up with appropriate solution• Takes place at level of perception, memory, or

cognition• Knowledge-based Mistakes – wrong solution because

individual did not accurately assess the situation.• Caused by poor heuristics/biases, insufficient info,

info overload• Rule-based Mistakes – invoking wrong rule for given

situation• Often made with confidence

TAXONOMY OF HUMAN ERRORSLIPS:

• Slips – Right intention incorrectly executed (oops!)• Capture errors – similar situation elicits action, which

may be wrong in “this” situation. Likely to result when:• Intended action is similar to routine behavior

• Hitting enter key when software asks, “sure you want to exit without saving?”

• Either stimulus or response is related to incorrect response• Hit “3” instead of “#” on phone to hear next

message, because “3” is what I hit to hear the first message

TAXONOMY OF HUMAN ERRORLAPSES & MODE ERRORS:

• Lapses – failure to carry out an action• Error of Omission (working memory)– Examples: Forgetting to close gas cap, failure to

put safety on before cleaning gun, failure to remove objects from surgical patient

• Mode Errors – Making the right response, but while in the wrong mode of operation• Examples: leave keyboard in shift mode while

trying to type a numeral, driving in wrong gear, going wrong direction because display was north-up when thought it was nose-up

FAULTY MEASURES UNDERTAKEN DURING THE HANDLING OF

EQUIPMENTS:1. Loose connections;

2. Faulty installation;

3. Improper grounding;

4. Defective parts;

5. Ground faults in equipment;

6. Unguarded live parts.

These Conditions lead to plant interruptions and disruption of processes and degrades Reliability.

• According to many safety and health laws, employers must provide a workplace where workers will not be exposed to hazards, where practicable.

• Workers must receive training, instruction, supervision, and information so they are not exposed to hazards.

Examples of FAULTY/ UNSAFE acts:

1. Failure to de-energize, Lockout and Tag-Out hazards during maintenance, repair, or inspections;

2. Use of defective and unsafe tools;

3. Use of tools or equipment too close to energized parts;

4. Etc..

CASE STUDIES ON THE FREQUENCY OF HUMAN ERRORS:

• Computer System Interruptions Caused By Human Errors

• Utility Distributions Interruptions By Human Errors

COMPUTER SYSTEM INTERRUPTION CAUSED BY HUMAN ERROR:

• A ten-year study at the University of Alberta’s central computer system was conducted analyzing the frequency of computer system interruptions caused by operator errors.

• A human or computer operator error is defined as an act or set of acts which results in a computer system interruption, and the system is restored to an operational state either by initial program loading or restarting.

• The computer system runs continuously 24 hours a day, except for maintenance periods early in the mornings on the weekends to minimize the impact of the scheduled interruptions on the users.

• The annual number of computer system interruptions caused by operator errors is shown in Fig (Next Slide).

YEAR OF STUDY:

• The total number of computer system interruptions caused by operator errors per year averaged approximately 25.

• Table 1 reveals the various percentages of interruptions attributed to the primary causes of computer system interruptions in which operators errors accounted 7.4% of computer system interruptions.

1. DAY OF THE WEEK OF COMPUTER SYSTEM INTERRUPTION:

• A ten year study of the average frequency of computer system interruptions per given day of the week confirmed belief of operators, as is shown in Fig. 2.

• The average frequency of computer interruptions was higher during the “weekdays” (i.e., Monday through Friday) than on the weekends, when the system loading was reduced.

• This supported the operators belief that “weekdays” were more prone to computer system interruptions than Saturday and Sunday.

DAY OF WEEK

2. TIME OF THE DAYOF COMPUTER SYSTEM INTERRUPTION:

• Many users of the computer system claimed that there appeared to be more interruptions in the morning than during the remainder of the day.

• The loading on the system peaked between 8–9 a.m., and the load dropped off between 4–5 p.m. and remained fairly steady for the remaining time periods.

• It is clear that the sudden increase in computer system loading and operator stress between 8–9 a.m. was directly correlated with a significant increase in the frequency of operator errors resulting in computer system interruptions.

TIME OF DAY

UTILITY DISTRIBUTION INTERRUPTION CAUSED BY HUMAN ERROR:

• The electric utility distribution system customer interruptions were recorded for the past 30 years by the Canadian Electricity Association (CEA) in Canada.

• It can be seen that the human element accounts for approximately 1.7% of the total number of distribution system interruptions.

• Other factors, such as scheduled outages, lightning, and defective equipment were the dominant causes of distribution system interruptions.

ELECTRIC UTILITY LOST TIME DUE TO INJURY ACCIDENTS:

• To measure the impact of injury accidents on productivity in terms of hours in the workplace, the CEA uses an index called the severity rate.

• The severity rate equals the number of calendar days lost due to injury accidents per millions of hours worked. Typical rates are shown in Fig. 5

• The severity rate remains fairly constant for several years, averaging about 500 days lost per million hours worked.

SEVERITY RATE

CLASSIFICATION OF HUMAN ERRORS ACCORDING TO SYSTEM

ORIENTATION:

• Human errors can occur at any stage in the life of a system.

• It occurs from the original design inadequacies, to installation deficiencies and operating and maintenance human anomalies.

Continued…

Design

Installation

Assembly

Inspection

Operating

Maintenance

Classification Of Human

Error

DESIGN ERROR:

• It can be attributed to the physical structure of a system with basically the following three types of inadequacies:

1. failure to implement human needs in the design.

2. assigning inappropriate functions to persons, e.g., lack of definition of primary work tasks;

3. failure to ensure the effectiveness of the man and machine component interactions.

• INSTALLATION ERROR:• This are primarily due to the failure to install

equipment by humans according to instructions or blueprints, assuming these drawings are correct, and poor workmanship when operating under severe time constraints.

• The inspection criteria of evaluation is dependent

upon the inspector’s knowledge of the system and the relation between its interacting parts.

• According to study an average inspection effectiveness is close to 85%.

• INSPECTION ERRORS:

ASSEMBLY ERROR:

• This errors are the result of poor workmanship. These errors are often discovered after the installation process when they disrupt scheduled system operations.

• Examples are:

1) use of incorrect component;

2) use of incorrect tools;

3) omitting a component;

4) improper connections;

5) improper handling of equipment.

OPERATION ERRORS:• This error is subject to human operating errors.

Situations that lead to these errors are as follows:

1) lack of proper procedures;

2) task complexity and overload conditions;

3) poor personnel selection and training;

4) operator carelessness and lack of interest;

5) poor environmental conditions.

MAINTENANCE ERROR:

• This errors are primarily due to the incorrect repair/replacement/service activities of equipment.

• Examples of maintenance errors are the following:

1) incorrect calibration of instruments, e.g., relays, computer controls, and sensors;

2) failure to follow maintenance schedules and procedures;

3) incorrect equipment cleaning procedures.

HUMAN RELIABILITY ANALYSIS

• Human Reliability Analysis – predict reliability of system in terms of probability of failure or mean time between failures (MTBF) when system is designed to work in parallel or series

.9 .9

.9

.9

Series

Parallel

Reliability = .9 x .9 = .81P(failure) = 1 - .81 = .19

Reliability = 1 – [(1 - .9) (1 - .9)] = 1 - .01 = .99 P(failure) = 1 - .99 = .01

TECHNIQUE FOR HUMAN ERROR RATE PREDICTION (THERP)

THERP components

1. Human Error Probability• Ratio of errors made to possible errors

2. Event Tree• Diagram showing sequence of events

• Probability of success or failure for each component

3. Other Moderating Factors• May add in multiplier to account for variables such

as experience level, time, stress, etc.

THERP EVENT TREE

a A

b\a B\a

SS

b\A B\A

FS

FS

FF

SeriesParallel

Series:P[S] = a(b\a)P[F] = 1 – a(b\a) = a(B\a) + A(b\A) + A(B\A)Parallel:P[S] = 1 – A(B\A) = a(b\a) + a(B\a) + A(b\A)P[F] = A(B\A)

P(successful task B given A)

P(unsuccessful task B given A)

P(success of task B given a)

P(Unsuccessful task B given a)

P(successful task A) P(unsuccessful task A)

Task A = first task

Task B = second task

ERROR PREVENTION / REMEDIATION

1. Task Design – design tasks with working memory capacity in mind

2. Equipment Design a) Minimize perceptual confusions – ease of

discrimination• Ex: airplane controls that feel like what they do

(flaps, wheels)b) Make consequences of action visible – immediate

feedback• Ex: preview window in some software programs

c) Lockouts – design to prevent wrong actions• Ex: car that will not let you lock door from outside

without keyd) Reminders – compensate for memory failures

• Ex: ATM reminds you to take your card

ERROR PREVENTION / REMEDIATION(Cont.….)

3. Training – provide opportunity for mistakes in training, so can learn from them

• Ex: Simulation

4. Assists and Rules – checklists to follow• Ex: Pilot pre-flight checklist

5. Error-tolerant systems – system allows for error correction or takes over when operator makes serious error

• Ex: Undo button

ACCIDENT-INJURY SEQUENCE MODEL :

• This Model provide a framework for identifying the possible root cause of electrical accidents.

• This Model provide a basis for developing accidents prevention and injury control strategies to minimize

1. impact of disruption to system operation.

2. occurrences of injuries.

SAFETY ANALYSISSequence for identifying potential hazards and recommendations for hazard

reduction: (Weinstein et al. 1978)

1. Task Analysis – How will product be used?2. Environment Analysis – Where will product be used?3. User Analysis – Who will use product?4. Hazard Identification – What is likelihood of hazard

with product?5. Generate Methods for Hazard Control – What might

eliminate hazards?6. Evaluate Alternatives – How will alternative designs

affect product performance?7. Select Hazard Control – Given alternatives, what is best

design to minimize hazards?

ACCIDENT INVESTIGATION LEVELS OF CAUSES

Management Safety Policy & DecisionsPersonal Factors

Environmental factors

Unsafe Act

Unsafe Condition

Unplanned Release of EnergyAnd/or

Hazardous Material

ACCIDENTPersonal Injury

Property Damage

BASICCAUSES

INDIRECTCAUSES(SYMPTOMS)

DIRECTCAUSES

SAFETY PROGRAMS

1. Identify risks to the company identify hazards, hazard controls, accident

frequency, & company losses due to accidents/incident claims

2. Implement safety programs, includes: management involvement, accident

investigation, recommendations for equipment, safety rules, personal protective equipment, employee training, safety promotion

3. Measuring program effectiveness evaluated by assessing changes in safety

behaviors, accident/incident rates, number of injuries or death, and number of days off due to injury

CONCLUSION / SUGGESTION:• Risk-Taking as a Decision Process

• People must know a hazard exists, know what actions are available, & know the consequences of the safe behavior vs. alternative behaviors

• Written Warnings and Warning Labels• Accurately convey the hazards of a product • Should include a signal word, info pertaining to the

hazard, consequences, & necessary behavior• Danger: Immediate hazard likely results in severe

injury• Warning: Hazard could result in injury• Caution: Hazard or unsafe use my result in minor

injury

REFERENCES:

• Human Element Factors Affecting Reliability and Safety, Don O. Koval and H. Landis Floyd, IEEE Transactions on Industry Applications, Vol. 34.

• IRACST- International Journal of Research in Management & Technology (IJRMT), ISSN: 2249-9563 ,Vol. 2, No. 1, 2012,Human Reliability Analysis: A review of the state of the art

• 4th European-American Workshop on Reliability of NDE - Th.4.A.1, Integrating Human Factors in Safety and Reliability Approaches by Babette FAHLBRUCH, TÜV NORD SysTec, Berlin, Germany http://www.ndt.net/index.php?id=8338

Thank You!!!