ENGINEERING ETHICS:

THREE CASE STUDIES

(Subtitle: EVERYTHING SHOULD BE AS SIMPLE AS

POSSIBLE, BUT NOT SIMPLER)

Victor Singer, P.E. (retired) Dan Schiffbauer, P.E.

Toshiba

OVERVIEW:

• Canons or Codes of Ethics

• Noteworthy Historical Background for Each Case In Point

– The Tacoma Narrows First Suspension Bridge: failed 1940

– The Silver Bridge (US Hwy 35 Ohio River Crossing): failed 1967

– The Shuttle Challenger: failed 1986

• Questions To Ponder For Each Case In Point:

– Are There Relevant Ethical Issues Or Just 20-20 Hindsight?

– When, If At All, Did Which Ethical Issue Come Into Play?

– If Errors Occurred, Were They Errors Of Judgment, Omission or Commission?

– Or Murphy’s Law Events - - Accidents In An Imperfectly Understood World?

– Who Should Have Done What, That He Didn't Do?

CANONS OR CODES OF ETHICS• NSPE, ASCE, ASME, AAES: Engineers shall hold paramount the safety,

health and welfare of the public . . . (Fundamental Canon)

• AIChE: Members shall hold paramount the safety, health and welfare of

the public . . .

• IEEE: We, the members of the IEEE . . . , do hereby . . . agree to accept

responsibility in making decisions consistent with the safety, health and

welfare of the public . . .

• AIAA: The AIAA member will have proper regard for the safety, health

and welfare of the public in the performance of his professional duties.

• AIA: Members should . . . thoughtfully consider the social and

environmental impact of their professional activities.

• ABA Model Code of Professional Responsibility: Canons:1. A lawyer should assist in maintaining the integrity and competence of the legal profession.

2. A lawyer should assist the legal profession in its duty to make legal counsel available.

3. A lawyer should assist in preventing the unauthorized practice of law.

4. A lawyer should preserve the confidences and secrets of a client.

5. A lawyer should exercise independent professional judgment on behalf of a client.

6. A lawyer should represent a client competently.

7. A lawyer should represent a client zealously within the bounds of the law.

8. A lawyer should assist in improving the legal system.

9. A lawyer should avoid even the appearance of professional impropriety.

CASE IN POINT: TACOMA NARROWS

FIRST SUSPENSION BRIDGE• Highway 16 Puget Sound Crossing between Tacoma WA and Kitsap Peninsula

opened to traffic 7/1/1940; collapsed 11/7/1940; 6-minute video of collapse

at http://www.youtube.com/watch?v=j-zczJXSxnw

from: http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)

VON KARMAN VORTEX STREET

(observed from space):• Wind blowing above the sea is disturbed by an island, creating a "vortex street."

Clouds serve as markers, allowing us to see the vortices in the flow downstream

of the island.

Von Karman Vortex Street in the atmosphere: SeaWiFS image courtesy of Orbimage,

Inc., SeaWiFS Project (Code 970.2) and Distributed Active Archive Center (Code 902) at

NASA's Goddard Space Flight Center, Greenbelt, MD

TACOMA NARROWS BRIDGE: before,

during and after failure• 3 hrs transverse flexural (up and down) vibration, amplitude 1.5 ft, 35 mph wind

• Wind rose to 42 mph, a midspan hanger cable broke (slipped), and the torsional

mode started. Frequency 0.2 Hz, 28 ft double amplitude

• Frequency associated with von Karman vortices at 42 mph wind: ~ 1 Hz

• Federal Works Agency's Failure Commission concluded: Vortex shedding unlikely

important because of the frequency difference.

• Violins teach that excitation with RANDOM frequency content produces

responses at resonant frequencies AND AT HARMONICS unless the vibrating

system provides substantial internal damping.

• Currently popular attribution: AEROELASTIC FLUTTER: jargon for stimulation of

multiple degrees of freedom CONCURRENTLY, A MURPHY’S LAW EVENT.

SIMILAR PHENOMENA

from: www.clarktesting.com

Stockbridge Damper (SCE 1928)

PROTECTION AGAINST MURPHY’S

LAW EVENTS• In general, interpolate within rather than extrapolate beyond

prior experience.

• Extrapolate in small steps, only where risk and benefits are balanced.

• Tacoma Narrows Bridge was a substantial extrapolation into the unknown.

• Much lower flexural rigidity and torsional rigidity than prior art, to reduce cost.

• Eminence of the designer - - Leon Moisseiff - - played role in suppressing criticism.

• Exception - - David B. Steinman, also an eminent suspension bridge designer, criticized the design at a 1938 meeting of the ASCE Structural Division.

• Othmar Ammann (Failure Commission member) wrote:– "The failure has given us invaluable information. . . [that] every new

structure that projects into new fields of magnitude involves new problems . . . [for] which neither theory nor experience furnish an adequate guide. It is then that we must rely on judgment. If errors or failures occur, we must accept them as a price for progress."

QUESTIONS TO PONDER– Are There Relevant Ethical Issues Or Just 20-20 Hindsight?

– When, If At All, Did Which Ethical Issue Come Into Play?

– If Errors Occurred, Were They Errors Of Judgment, Omission or Commission?

– Or Murphy’s Law Events - - Accidents In An Imperfectly Understood World?

– Who Should Have Done What, That He Didn't Do?

SECOND CASE IN POINT: THE SILVER

BRIDGE• US Highway 35 Ohio River Crossing, Point Pleasant WV to Kanauga Ohio.

– completed 1928, collapsed 12/15/1967 center span 700 ft, side spans 380 ft each,

deck width 28 ft

from: http://en.wikipedia.org/wiki/Silver Bridge

SILVER BRIDGE

• 46 dead, 2 missing (never found)

HERCILIO LUZ BRIDGE• Florianopolis, Brazil

– (26 deg S latitude) center span 1113 ft. Opened 1926, closed 1982, re-opened

(pedestrians) 1988, closed 1991

• Designers: David B. Steinman and Holton D. Robinson

– Using eyebar chain as upper chord of stiffening truss reduced weight and cost.

– American Bridge Company proposed using their "special" 1060 carbon steel eyebars

heat-treated to over 2X strength of the 1020 ASTM A-7 in common use.

– Steinman dissociated his firm from further connection with the project.

SILVER BRIDGE: concept &

proportions copied from Florianopolis• For main span 2/3 as long, chain tension force was about half as large, allowing chains

with only two heat-treated 1060 steel eyebars rather than four as on Florianopolis.• If one outer eyebar breaks, pin cannot sustain unsymmetrical load; bridge comes

down

• Eyebars 12” x 2”, Eye dia 28 in. Pin dia 11 inches• Heat Treat: ST 875 degC, WQ, temper 625 degC 2 hrs.• Average eyebar properties: Ftu 120 ksi, Fty 81 ksi, El >20%, R/A >45%, CVN 2 to 3 ft

lbs at 32 degF, KIc 46.4 ksi root inch• Other steel shapes and plate (1020 carbon steel, ASTM A7-24) Ftu 58.2 ksi, Fty 31.7

ksi, El 20.7%, R/A > 50%, CVN > 15 ft lb at 50 degF, KIc ~100 ksi root inch• Eyebar allowable stress 50 ksi (67% of min required elastic limit)

Ignorance is Truly Bliss• Only one recovered eyebar had a broken head

• Fracture Surface, lower side: corner crack 0.28 inch long (parallel to 2 inch thickness), and

0.12 inch deep radially.

• Technology enabling quantifying the relationship between flaw size and failure load didn't

yet exist in the 1920's when Silver Bridge was designed.

• 1920’s era brittle fracture provisions for steels for buildings and bridges commonly

reflected a 15 ft lb minimum CVN (Charpy Vee Notch Impact Test)

• Eyebar steel, at 2X the strength, provided less than 20% as much fracture energy

• Steinman’s view (evidently): Stronger eyebars either too much extrapolation from prior

experience or too little fracture energy for Florianopolis, as far from equator as Miami and

much warmer than Kanauga.

SILVER BRIDGE: post-mortem• Found original stress analysis reasonably accurate

• Evaluated actual loading at time of failure to estimate actual load on failed

eyebar.

• Conducted extensive material testing program, including modern fracture

toughness tests and related crack growth rate quantifications, and scale model

testing program.

• Final Highway Accident Report NTSB Report SS-H-2 (adopted 12-16-1970):

– Fig 36: approximate positions of all vehicles on the bridge at time of failure.

– Westbound lane 1/3 empty, eastbound lane more than half empty.

– Page 98: "the probability of 100 percent of design stress is quite remote."

– Failed eyebar head obviously loaded to actual capability when it failed.

– The state-of-the-art circa 1920’s lacked recognition of potential premature - - flaw-

induced - - failure in brittle materials at low temperatures.

– Fracture cause: a flaw grew over 40 years to critical size by stress corrosion and

corrosion fatigue. Which was dominant is unknown.

– No indication main member deterioration by rusting to a point of inadequacy under

intended or actual loading.

QUESTIONS TO PONDER– Are There Relevant Ethical Issues Or Just 20-20 Hindsight?

– When, If At All, Did Which Ethical Issue Come Into Play?

– If Errors Occurred, Were They Errors Of Judgment, Omission or Commission?

– Or Murphy’s Law Events - - Accidents In An Imperfectly Understood World?

– Who Should Have Done What, That He Didn't Do?

THIRD CASE IN POINT: SHUTTLE

CHALLENGER

What SHOULD happen:

• SPACE SHUTTLE DISCOVERY

at STS-120 Launch

What DID happen:

• SPACE SHUTTLE CHALLENGER

at SPS-25 Launch Jan 28, 1986

BACKGROUND: Space Shuttle

Program Overview

• Vehicle Architecture: Shuttle's

"Stages In Parallel" architecture

was a substantial departure from

Apollo and Mercury "Stages In

Series" architecture.

• Re-Usable Orbiter objective made

Crew Capsule Jettison feature of

Apollo and Mercury programs

more difficult than before.

• NASA Decision: NO CREW

CAPSULE ESCAPE SYSTEM FOR

SHUTTLE

APOLLO flight vehicle

BACKGROUND Space Shuttle

Program Overview cont’d.

• Funding Strategy: Seek Congressional approval by earmarking at least one component supplier contract for each US Senatorial and Rep District in the country.

• Delaware got space suits, Wisconsin got SRM steel cases, Minnesota got phenolic resin impregnated carbon cloth, Virginia got rayon for white woven cloth (carbon cloth precursor), Nevada got ammonium perchlorate oxidizer for solid propellant, etc.

• Congressional direction to NASA: YOU TELL US that revenue from commercial flights will cover the program development costs.

– Interpretation: "You tell us" more important than whether or not it's true.

– Responses: 1) Flight schedule large enough to recover program development costs; 2) Intense program-long focus on costs.

• Original launch schedule built from "modest" start to SIXTY flights/year; peak launch rates actually achieved: 9 in 1985 and 8 in 1997.

• All ground support systems designed AND BUILT to support 60 flights/year schedule.

SUBTLE DEMONSTRATION OF NASA

“SHOP CULTURE”• Projected 60 flights per year schedule is one flight every six days.

• Time in orbital flight much longer than time during ascent.

• Potential for damage by collision with space junk (natural or otherwise) during

ascent or orbital flight, precluding normal return, should be among design

considerations.

• Obvious solution: Standing policy NOT to fly Flight "X" until Flight "X + 1" is

within six days of flight-ready.

• No such policy was in effect when the Shuttle Columbia failed re-entry (2/2003).

• After Columbia, it was implemented for only one of the several additional flights.

• Credible reason: In the year such a policy becomes effective, implementation

requires paying for one more total vehicle build-up than the number of flights.

• Cost impact first year, no impact thereafter.

• MANAGEMENT DECISION: Do it NEXT year. Cost out-ranks safety.

CLEVIS JOINT CROSS SECTION

(schematic)

A - steel wall thickness 12.7 mm, B - Primary O-ring, C - Backup O-ring,

D - Cork cover band, E - insulation, F - insulation, G - carpeting,

H - sealing paste, I - propellant

IMPLICATIONS OF SPACE SHUTTLE

SRM SERVICE TEMPERATURE• NASA specification: demonstrate capability to operate between +40 degF and

+90 degF.

– SRM Thermal mass judged sufficient to bridge excursions higher or lower.

– Lowest temp full scale demo, at +53 degF, showed primary O-ring blow-by.

– Effect of adjacent orange tank for cryogenic fuel and oxidizer unrecognized.

– Orange tank caused convection; SRM case temp was often below +40 degF

• SRM clevis joint was originally proportioned to INCREASE O-ring squeeze with

rising pressure.

• After case fab was well under way, NASA initiated weight reduction to increase

payload by reducing SRM case cylinder thickness between clevis joints. This

changed clevis joint behavior, DECREASING O-ring squeeze with rising pressure.

• O-ring (artificial rubber) stiffens with decreasing temp,

• Squeeze loss during pressurization prompted intense experimental inquiry into

O-ring material behavior: Would prior squeeze relax fast enough to maintain seal

during ignition pressurization and thereafter.

• Result: Yes (on paper) at +40 degF and higher, but 53 degF was lowest actual

fully credible verification from an early 1985 flight.

PRE-LAUNCH ACTIVITY AT THE CAPE• Evening before launch, at Readiness Review Meeting, anticipated weather for

1/28/1986: 29 degF at 9 am, 38 degF at 2 pm (without convection effect)

• MTI lead on-site rep presented charts leading to first (engineering)

recommendation: "O-Ring temp must be 53 degF (or greater) at launch."

• NASA on-site reps asked for and got MTI higher management telecom

concurrence. After off-line conference, top management in Utah withdrew earlier

objection.

• Launch day morning observations: ICE EVERYWHERE ! !

– Local ambient air temp +26 degF

– ICICLES HANGING FROM AFT SEGMENT STIFFENING RINGS ! !

– Hand-Held Infrared Pyrometer measurements on one of steel cases: near aft field joint:

+9 degF, on aft skirt +7 degF

– Ice Team informed Mission Management Team soon after 9 am.

– No MMT discussion because measurements were for Engineering Information only, not

part of formal Launch Commit Criteria

– Ice Team 10:30 am inspection disclosed ice still on one of the SRB's

– Houston Mission Control reported that trajectory analysis of ice falling from orange

tank during flight would not impact orbiter

• Launch was at 11:38 am

Failure on the Pad

THE GREEN BALL THEORY(title of Chapter 26 in "Truth, Lies and O-Rings: Inside the Space Shuttle Challenger Disaster" Allan J. McDonald with James R Hanson)

• Conversation, Al McDonald and Richard Feynman, physicist, Nobel Prize winner, Rogers Commission member, at impromptu May 1986 lunch: Summary of 13 pages of text:

– Feynman: Why did Morton Thiokol (MTI) management change their minds after their initial recommendation not to launch?

– McDonald: Because of the Green Ball Theory.

– Feynman: What's the Green Ball Theory?

– McDonald: Management considerations: No signed contract for the next SRM buy; and NASA announced intent to seek a second source for SRM’s.

– Feynman: So what does that have to do with a Green Ball Theory?

– McDonald: What do you have when you have a green ball in your left hand and another green ball in your right hand?

– Feynman: I don't know. What DO you have?

– McDonald: Complete and absolute control of the Jolly Green Giant!

QUESTIONS TO PONDER– Are There Relevant Ethical Issues Or Just 20-20 Hindsight?

– When, If At All, Did Which Ethical Issue Come Into Play?

– If Errors Occurred, Were They Errors Of Judgment, Omission or Commission?

– Or Murphy’s Law Events - - Accidents In An Imperfectly Understood World?

– Who Should Have Done What, That He Didn't Do?

TWO MESSAGES TO RECOGNIZE:• We understand much;

• We don’t yet understand more.

AND REMEMBER WHAT THE SECOND ONE TEACHES:• Be cognizant of the need for further learning;

• Be attentive to what you see along your path.

LEARNING IS LIKE DRIVING AT NIGHT:• Our headlights illuminate only 300 feet of the road ahead;

• With continuing attention to details, we can travel far, reasonably safely.

POST-SCRIPT: COINCIDENCES INTER-

RELATE THE CASES IN POINT• The Tacoma Narrows Bridge failure has been attributed to aeroelastic flutter.

– Theodore von Karman, an aerodynamicist, long before the 1940 event, had quantified the fluid flow condition later known as a von Karman vortex street, including its periodicity. He served in the failure investigation.

– David B. Steinman, a structural engineer, strongly criticized the design before it was built, perhaps because it substantially extrapolated beyond prior experience.

• The Silver Bridge failed because its eyebar steel was twice as strong but ten times as brittle as steels conventionally used in bridge and building construction.

– Its design was copied from a similar David B. Steinman bridge in a warmer climate.

– Steinman dissociated himself from that design when his client chose to use high strength steel in its eyebars, to reduce cost.

• The Shuttle SRB's were built by a successor to Thiokol Chemical Corporation, which went into the rocket motor business when GALCIT's JPL started using Thiokol's polysulfide polymer to control the burn rate of black powder.

• JPL at the time was headed by Theodore von Karman, who coined the Jet Propulsion Lab name.