Safety
The engineers role in
risk reduction
Peter Gostomski & Ken Morison
Chemical & Process Engineering
Space shuttle disasters
► Challenger blew up on take off (1986)
O-ring on booster rocket failed
Leaking fuel ignited, liquid H2 tank exploded
► Columbia destroyed during reentry (2003)
foam damaged wing tiles during take-off
tiles failed during reentry
Longford gas processing plant (1998)
► Longford (Esso) supplies energy to Victoria, AU
► Energy supplies out for 2 weeks
► $3 million fines + compensation
► $500 million law suit for lost revenue.
► 2 workers died
Firestone tyre recall (2000)
► Firestone recalls 10 x 106 tyres in 2000
► Tread separation causes rollover accidents
► 40 – 80 deaths attributed to bad design
► Lost sales = $350 million
► Fines = $41 million
► Ford cancels contract
Concorde crash (2000)
► Concorde crashed on take-off
► 113 people died
► Debris on runway punctured tyre, chunks of
rubber punctured fuel tank
► Fire caused loss of power
World Trade Center (2001)
► Two fuel-laden jets crashed into WTC towers
► Fire caused support structure to fail
► Towers collapsed
► 2,792 people died
Power Outage – North America (2003)
► power overload caused supply to fail
► chain reaction caused power loss in eastern US
and Canada.
► 50 million without power
► Responsibility? Costs?
► Auckland CBD lost power on/off
for two months in 1998
Engineers – what role in safety?
► Engineers solve problems
► The cause of all problems are solutions
Engineers cause a lot of problems?
NO!
► Engineers very good at preventing disasters
Engineers vs Doctors
► Engineers try to fence off the top of the cliff
► Doctors wait at the bottom of the cliff
Engineering versus other careers
► All professional careers can affect peoples
lives
Commerce large scale redundancy
Law innocent people to jail
Medicine misdiagnosis
Engineering activities in safety
► Find the problem:
What will explode? What part will fail? How much force
on impact?
► Measure the problem:
Determine probability that part fails & alarm fails
Toxic gas released how many people exposed?
► Solve the problem:
New designs
New procedures
Safety Goals
Prevent:
Death/injury to workers
Death/injury to the general public
Damage to facilities
Damage to surrounding property
Damage to the environment
Key Definitions
Hazard – physical situation that can damage:
people
plant
environment
Risk – likelihood of hazard occurring
Risk = hazard * probability * consequence
Risk = hazard * probability * consequence
► Flammable solvent vs nonflammable solvent
= different hazard level
► Bridge over a 5 meter gorge vs 30 m gorge
= different hazard level
In both cases risk is lowered
by removing or lowering hazard
Risk = hazard * probability * consequence
Dangerous chemical reactor is completely
automated.
= no risk to workers Same hazard,
risk to neighbours? same probability,
different
risk to equipment? consequences
risk to environment?
Ladder example
Risk = hazard * probability * consequence
Virtually no activity is risk free!
Can’t eliminate all hazards
Can’t make probability zero
Can’t eliminate all consequences
As long as all three components exist,
risk exists!
Risk
Engineers decrease risk by:
► Identify/eliminate hazards
► Estimate/lower probability
► Estimate/lower consequence
When is risk low enough?
Risk
What is acceptable risk?
► societal/political decision
► engineers identify, calculate, lower risk
► society decides acceptable level of risk
Problem: 1 – Not everyone realises risk ≠ 0
2 – Public perception depends on situation
Risk – acceptable levels
Public perception of risk depends on a number of
features
► Control – individual control, avoidable, survivable
► Knowledge – understanding, observable, familiar
► Magnitude – number of people exposed
► Others factors
Unknown risk
1
solar power genetics
nuclear
marijuana
power
pesticide
controllable uncontrollable
risk vaccine risk
0
-1 valium 0 jets 1
nuclear
bicycle smoking weapons
crime
cars
alcohol
guns
-1
Known risk
Magnitude
7 people died in the Challenger Space Shuttle
113 died in the Concord crash
2792 died in 9/11
About 1.2 people die in each fatal car crash
400 000 people die in car crashes
worldwide each year
Estimate risk (numerical)
Fatal Accident Rate (FAR)
FAR = deaths/1000 people/105 hours
105 hours lifetime 35 years (8 hr day)
Industry FAR
Chemical industry 2
Manufacturing industry 4
Coal mining 8
Offshore oil and gas 62
Rock climbing 4000
FAR example
How dangerous is being an engineering student?
Over the last 10 yrs we have had 22 deaths
1 death terrible hacky sack injury
3 deaths American lecturer shot rude students
1 death sleeping student fell off chair
2 deaths engineering cafeteria food poisoning
15 deaths listening to boring lectures
FAR example
22 deaths over 10 yrs
900 students/yr = 9,000 students total
Death rate = 22 deaths/9,000 students/10 years
Death rate = 0.000244 deaths/student/yr
FAReng = 0.000244 * 1000 people* 35 years
FAReng = 8.6
FAR
Simple measure of safety
1. Historical analysis of industry or activity
2. Prediction tool
Estimate FAR for building a new bridge
Compare estimate to bridge building
industry average
Estimate risk (numerical)
Fatal Accident Rate (FAR)
FAR = deaths/1000 people/105 hours
105 hours lifetime 35 years (8 hr day)
Industry FAR
Chemical industry 2
Manufacturing industry 4
Coal mining 8
Offshore oil and gas 62
Rock climbing 4000
FAR – Rock climbing
FAR = 4,000
• per 1,000 people for 35 yrs
• People that fall are replaced
A rock climber ascends
a basalt column in an
Auckland quarry.
FAR – Rock climbing
100 people in a climbing club spend 10 days/yr at
6 hrs/day climbing, 1 person dies over 5 yrs
10 days/yr * 6 hrs/day * 5 yrs = 300 hrs
Death rate = 1 deaths/(300 hrs * 100 people)
= 0.000033 deaths/person-hr
Far = Death rate * 1000 people * 105 hrs
= 3,333
Risk Reduction (for discussion)
► Travelling by plane is more hazardous than by car.
► Travelling by car is riskier than by plane.
Traveling is more hazardous by plane
than by car.
Cars Planes
► Ground level ► 13,000 meters
► 100 km/hr ► 1,000 km/hr
► normal temp & press. ► Low temp. & pressure
► 1 – 6 people ► 200 – 400 people
► 40 – 80 litres of fuel ► 100,000 – 200,000
liters of fuel
Traveling by car is riskier than by plane.
Planes Cars
► High quality parts ► The Warehouse
► High redundancy ► Little redundancy
2 engines, 2 pilots, etc 1 engine, 1 driver, etc.
► Many safety devices ► Some safety devices
Sensors, alarms Sensors, alarms
► High maintenance ► Maintenance?
Traveling by car is riskier than by plane.
Planes Cars
► Preflight checklist ► Predriving checklist(?)
► Airport design ► Parking lot design
► Traffic control ► Traffic control
Air traffic controllers Traffic lights
► Training ► Training
Flight simulators PlayStation/Xbox
Pilot licence Watching Mum or Dad
Car licence
Planes versus Cars – The risk?
FARCar = 30 FARPlane = 40
Risk per 109 km
RiskCar = 4.4 RiskPlane = 0.2
www.rvs.uni-bielefeld.de/publications/Incidents/DOCS/Research/Rvs/
Article/probability.html
NZ risk about 10 per 109 km
Risk Reduction Strategies
► Procedural (people activities)
procedures, alarms, training
► Active (automatic devices)
switches, relief valves, auto-shutdown, sprinkler systems
► Passive (no moving parts)
Stronger fuel tank, less fragile heat tiles
► Inherent (fundamental hazard)
ground travel instead of flying, water instead of toluene
Simplify process
Summary
► Safety - prevent damage to
People Equipment Environment
► Risk = hazard * probability * consequence
identify haz. measure prob/conseq. design solut.
Engineers lower risk
Society decides acceptable level
► Risk reduction:
procedural active passive inherent