Safety

System & Scene

Overview

• Safety Terms

• Hazards

• Hazard Lists

• Worst Case Conditions

• Hazard Characteristics

• Analysis

• Sumary

Safety Terms

• Hazard: Condition with potential to injure

• Danger: Exposure to hazard

• Damage: Severity of injury

• Risk: Probability of occurrence times damage (RHI)

Hazard

• Types:– Primary Hazard: Immediate damaging causing– Initiating Hazard: Starts event sequence leading

to damage ( rope abrasion leading to reduced tensile strength and ultimate failure)

– Contributing Hazard: Subordinate hazard adding to the ultimate failure of a system ( inadequate Belay System rigging, fails in Main failure)

Hazard Lists

• Hazard lists are the first step in recognizing hazards and preventing damage

• Development: (best lists use combination)– Past experience– Theoretical possibility ( What can you

imagine)– Predictive testing ( rope testing… load,

abrasion, UV etc)

Safety & Murphy’s Law*

• Worst case scenario – Max loads– Most serious outcomes– Combined events ( UV, Abrasion, Overloads)– Ignores probability of occurance

• *“If something can go wrong it will”– “It will go wrong at the worst possible time”

Categories of Hazards

• Inherent Hazard: Properties or characteristics of system make it hazardous (High angle rope systems, working hi-voltage)

• Failures (material or human): Rope fails under load ( material defect), knot lets go ( tied incorrectly)

• Environmental stresses: Lightning strike, Wind shear, UV degredation, “Acts of God”

Accidents

• Failure to prevent damage– Almost all accidents can be traced to human

error (although not necessarily the primary hazard event).

– May not be on the part of the immediate victims ( may be dissociated in time and space from accident event, for example: poor rope maintenance/inspection)

Human Error

• 2 types ( also like hazards may be primary or contributory)– Predictable: “could have been expected”

usually driven by:• Fatigue

• Sensory limitations ( poor visibility etc)

• Physical limitations ( coordination etc)

– Random: “unpredictable” unexpected or unusual sequence of events, no history of similar occurrences, driven by a rare or unique event

Minimizing Human Error

• 2 Man Concept– Credited to the Military to minimize potential

for human error in nuclear system procedures– Probably goes back to the first attempts at

controlling risky processes.

• Training ( most human error occurs under stress and haste, training minimizes error under stress

Accidents and Human Error

• Accidents rarely occur due to willful actions

• Most are situations in which human capabilities are inadequate or overwhelmed by the “Need for rapid response to a critical situation”– Inadequacies can be permanent or transient

• Permanent: Physical limitations, lack of training

• Transient: Fatigue, communications breakdown

Hazards and Accidents

• Accidents occur when”

Hazards potential to cause damage reaches a probability of 1

• This leads to 2 obvious approaches to safety:– Minimize hazards– Reduce probability

Accident Analysis Vs. Hazard Analysis

• Accident Analysis is Post Mortum

• Hazard Analysis is predictive in nature

• Hazard Analyses are conducted on systems

• A system is all the components which combine to perform a function…. Rope, anchors, prussics, people!

Safety Factors & Margins

• Safety Factors are a ratio of strength to expected stress

• Safety Margins are the difference between max stress and min strength

Hazard Analyses

• Qualitative- non-mathmatical– A review of potential hazards, excluding

probabilities

• Quantitative- must be preceded by qualitative review– Probability of occurrence of a specific failure

mode, based on history or speculation.

Hazard Analysis

• Requires review of:– Mission requirements– Performance capabilities– Operational sequence– Environmental impacts– Codes, regulations, specifications, standards

Probability• Probability is the expectancy of frequency with

which an event will occur in a specific number of trials

• Determined by– Actuarial methods ( using historical data)

– Experimental methods (test and count failures)

– Predictive models ( usually based on similarity to known systems )

• Heads/Tails 100K trials 50K heads.. Next flip 50/50.. Individual event is could be any outcome

Failure Modes, Effects, & Capability Analyses- FMECA

• Review of component failure modes– Fails How?

• Effects of such failure will have on the rest of the system

• Establish which part failures would have critical (catastrophic) impacts on the system

• Calculate the probability of such failures

RHI- Relative Hazard Index

• RHI- probability of event occurrence times expected damage if event occurs

• A quick way to prioritize safety issues

Risk

• Risk is a method of comparing relative hazard exposures

• RHI is a risk measure

• Hazard analyses which include both qualitative hazards and quantitative probability of hazard damage can also be used to rank or compare risks

Summary

• Safety is “No Accident”

• Prevent accidents by:– Mitigating hazards– Mitigating probability of occurrences

• Evaluate hazards thru analyses

• Compare Risks between options