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Copyright © 2011 Underwriters Laboratories Inc. ® All rights reserved
HAZARD ANALYSIS:Hazard Based Safety Engineering
&Fault Tree Analysis
Tom Lanzisero, UL
Slide 2
What do we mean by Safety, Risk, Harm and Hazard?
What is Hazard Based Safety Engineering (HBSE)?
What is Fault Tree Analysis? How do these Hazard Analysis
tools help us meet our Safety Objectives?
Slide 2
Hazard Analysis
Slide 3
Keep it Simple, but…
“Everything should be made as simple as possible, but not one bit simpler.”
Albert Einstein
Slide 4
SAFETY - freedom from unacceptable risk RISK - combination of the probability of
occurrence of harm and the severity of that harm HARM - physical injury or damage to the health of
people, or damage to property or the environment HAZARD - potential source of harm
Example Definitions (International Safety Community):
ISO/IEC Guide 51, Safety aspects – Guidelines for their inclusion in standards
ISO – International Organization for Standardization; IEC – International Electrotechnical Commission
Slide 4
Safety Terms
Slide 5
Expressing Relative Risk
Pro
ba
bili
ty o
f Ha
rm (
P)
Severity of Harm (S)
P x S = constant P x S = constant
Higher
Risk
Higher
Risk
Lower
Risk
Lower
Risk
Slide 6
Hazard Analysis
Hazard Analysis - Determine what harm can occur and how– What: Harm types, degrees, potential sources (hazards)– How: Harm mechanisms, conditions and causes
Hazard Based Safety Engineering (HBSE)– Systematic process - design / evaluate– Addresses conditions and mechanisms: harm protection– Analysis tools include 3-Block Model and FTA Model
Fault Tree Analysis (FTA)– Graphical representation of causes of a fault (undesirable event)– Covers conditions, events, root causes and logical relationships– Analyzes harm and protective measures, strategies and priorities
Slide 7
Surroundings Transfer Susceptible Entity
General Model for Harm
HARM: due to improper transfer between a susceptible entity and its surroundings
Harm to:PersonsProperty
Environment
Too much / too fast(Hazardous)
Too little / too slow(Needed)
Energy /Material
Slide 8
Model for Harm from a Hazard
HazardousEnergy,MaterialSource
TransferSusceptible
PersonProperty
Environment
HAZARD(Potential source of Harm)
HARM(Injury / damage)
Slide 9
HBSE 3-Block Model for Injury
Mechanical (kinetic) energy(e.g., moving part)
Electrical energy(e.g., live part)
Thermal energy (heat)(e.g., hot surface)
Contact
Contact(current thru
body impedance)
Contact(conductive heat flow)
Laceration to hand(minor to severe)
Ventricular fibrillation(lethal)
Skin burn(1st, 2nd, 3rd degree)
HazardousEnergySource
TransferMechanism
Susceptible Body / Part
E.g.,
Slide 10
Protection Strategies
HazardousSource
Transfer SusceptibleEntity
Eliminate (inherently safe), limit, or control
the hazard
Eliminate, limit or control the
transfer (exposure)
Decrease the susceptibility of
the entity to harm(as applicable)
Slide 11
ENERGY TRANSFERHAZARDOUS
ENERGY
INJURY
BODILYEXPOSURE
AND
Fault Tree Analysis (FTA)
HBSE Fault Tree for InjuryTop Level Model
Slide 12
ENERGY TRANSFERHAZARDOUS
ENERGY
INJURY
BODILYEXPOSURE
AND
Hazardous
Energy
Source
Transfer
MechanismBody
Susceptibility
Fault Tree with 3-Block Model
Slide 13
Expanding the Fault Tree Model
Top Event(System Fault)
Minimum,concurrent,
necessary & sufficient
conditions
Primary Events(Root Cause)
From generalto incrementallymore specific
categories
ENERGY TRANSFERHAZARDOUS
ENERGY
INJURY
BODILYEXPOSURE
AND
OROR
Hazard DueTo Fault
~~~~AND
….
ANDAND
….
~~~~AND
….
ANDAND
….
Root cause failures of Protective Measuresintended to eliminate, limit or control
Energy / Material Transfer
Root cause failures of Protective Measuresintended to eliminate, limit or control
Hazards
IntermediateConditions / Situations /
Events
Individualor In
combination
Hazard in Normal Condition
Hazard in Normal Condition
Slide 14
HBSE Fault Tree Model for Injury
ENERGY TRANSFER
INJURY
AND
INADEQUATEPERSONAL
SAFEGUARD
PERSONALSAFEGUARD
FAILURE
NOPERSONAL
SAFEGUARD
OR
INADEQUATEPERSONALAVOIDANCE
AVOIDANCENOT
POSSIBLE
AVOIDANCENOT
ATTEMPTED
OR
BODILYEXPOSURE
AND
INADEQUATEEQUIPMENTSAFEGUARD
EQUIPMENTSAFEGUARD
FAILURE
NOEQUIPMENTSAFEGUARD
OR
INADEQUATEEQUIPMENTSAFEGUARD
EQUIPMENTSAFEGUARD
FAILURE
NOEQUIPMENTSAFEGUARD
OR
HAZARDOUSENERGY
AND
(EVENT)
OR
(EVENT)
OR
Slide 15
ENERGY TRANSFER
INJURY
AND
INADEQUATEPERSONAL
SAFEGUARD
PERSONALSAFEGUARD
FAILURE
NOPERSONAL
SAFEGUARD
OR
INADEQUATEPERSONALAVOIDANCE
AVOIDANCENOT
POSSIBLE
AVOIDANCENOT
ATTEMPTED
OR
BODILYEXPOSURE
AND
INADEQUATEEQUIPMENTSAFEGUARD
EQUIPMENTSAFEGUARD
FAILURE
NOEQUIPMENTSAFEGUARD
OR
INADEQUATEEQUIPMENTSAFEGUARD
EQUIPMENTSAFEGUARD
FAILURE
NOEQUIPMENTSAFEGUARD
OR
HAZARDOUSENERGY
AND
(EVENT)
OR
(EVENT)
OR
Fault Tree Protection Strategies
ELIMINATETHE
HAZARD
1
GUARDAGAINST THE HAZARD
(Energy / Exposure)
2
WARNOF
HAZARD
3
Slide 16
Thanks! Questions?
Thomas Lanzisero, P.E.Sr. Research Engineer
[email protected]+631-546-2464
For more, please see Applied Safety Science and Engineering Techniques (ASSETTM)Paper published and presented at 2010 IEEE Symposium on Product Compliance
Engineering, sponsored by IEEE Product Safety Engineering Society:
http://www.uluniversity.us/common/ncsresponse.aspx?rendertext=thoughtleadership#research_development
Underwriters Laboratories (UL)1285 Walt Whitman Rd
Melville, NY 11747-3081 USAwww.ul.com