Ian Simpson

www.hsl.gov.ukAn Agency of the Health and Safety Executive

www.hsl.gov.ukAn Agency of the Health and Safety Executive

Tower Crane Incidents Worldwide

Ian Simpson – Principal Specialist Inspector, HSE

An Agency of the Health and Safety Executive

OBJECTIVES

• To identify worldwide Tower Crane accidents 1989 to 2009

• Obtain where possible the cause(s) of each accident identified

• Use the information to advise/guide the UK Tower Crane industry to help improve safety


CRANE TYPES

• Confined to tower cranes commonly found on UK construction sites.

• Only major accidents resulting in the collapse of the crane considered

• Does not include– Mobile Cranes– Self Erecting Tower Cranes– Tracked Crawler Cranes– Dockyard Cranes – Gantry Cranes & Container Cranes


CRANE TYPES

LUFFING JIB CRANE

CONVENTIONAL TOWER CRANE


InternetWebsites of trade/industry magazines

craneaccidents.com & towercraneaccidents.blogspot.com

Websites of private individuals with some connection with

the industry (both U.S. based)

Websites of media local to the accident e.g. New York

Times

SOURCES OF INFORMATION


• No single source of accurate information identified

• “Trade” websites tend to be Ok for the initial report & will follow up with further detail when available

• The two private websites often inconsistent with the “trade” websites and are prone to (usually well meaning) speculation.

LIMITATIONS/DIFFICULTIES


• Not all the websites have knowledge of all the accidents. Some accidents are given on one website but not another.

• Local media usually reports in the immediate aftermath of the incident and details can be vague & inaccurate

• Geographic locations. Remote countries with less developed health & safety cultures tend not to be as well reported (investigated ?) as U.S.A. & Europe




This can be frustrating

Zibo City, China Battersea

• Visually similar accidents. Top of the crane has parted from the mast section at the slewing ring joint. Lack of detailed information from the China accident prevents accurate comparison


• 54 accidents resulting in the collapse of the tower crane involved identified since 1999.– Information prior to 1999 very scarce

RESULTS


• These split into the following categories:– Erection/Dismantling or Extending (climbing) the

crane– Strong Winds or Extreme Weather– Foundation Problems– Mechanical Issues (including safety & control

systems)– Misuse of the Crane, e.g Overload, Collision etc– No details verified in the research to explain the

collapse

RESULTS


20

10

7

6

3

8

Erection/Dismantling/Extending

Extreme Weather

Foundation Issues

Mechanical Issues

Misuse

Cause Unidentified

RESULTS

54 TOTAL


EXAMPLES OF ACCIDENTS

• Erection/Dismantling or Extending

New York – March 2008





• Cause of accident focused on the number and condition of the lifting slings used to lift/support the tie in collar

• Four slings were used instead of eight recommended by the manufacturer.

• Old slings were apparently used with no prior inspection despite four new slings being offered by the construction manager to the rigging crew

• Sling protection not used





DAMAGED/FAILED SLING

TIE IN COLLARS





• Nothing technically wrong with the crane itself

• Accident centred on competence, procedural, communication issues & condition of lifting equipment in use

• These factors not confined to Tower Cranes or foreign countries



• Foundation Issues

Seattle – November 2006





• Crane mast section severed approximately 15 feet from the base

• The foundation was an uncommon design consisting of steel I section cross beams supported by four concrete pillars

• Site workers raised issues concerning the crane before the accident. They reported that the foundation “creaked & groaned far more than usual”.




• Photographs of the crane taken before the accident show that the crane appeared to be leaning

• Accident attributed to failure of welded/bolted joints in the foundation steelwork

• This resulted in the crane leaning and overstressing the bottom of the mast section






• Accident centred on design & manufacturing issues of the foundation itself and communication issues

• Had the concerns raised by the site workers been acted on could the accident have been avoided ?

• Again, these issues not unique to the tower crane industry or foreign countries




Singapore – February 2008PIN

GROUND ANCHOR ATTACHED TO CONCRETE FOUNDATION BLOCK

MAST SECTION LEG

• More conventional foundation arrangement. No accurate details concerning the root cause. It appears as if the ground anchors have failed and the pins have pulled through them.



• Mechanical Issues

New York – May 2008





• Crane involved was a “Kodiak” at least 24 years old

• Production of Kodiak cranes ceased prior to the accident

• Investigation showed that the accident was due to failure of a welded repair to the slewing ring support structure at the top of the mast section.





• Accident raised issues of use & maintenance of aged plant:-

• Why did the slewing ring support structure require repairing in the first place ?

• Who technically evaluated/authorised the welded repair technique and inspection criteria/standards (if any) ?

• Was the repair carried out to the required standards ?

• These sort of issues not confined to the tower crane industry or foreign countries



• Mechanical Issues (Control System)

Rotterdam – July 2008





• The crane was lifting a heavy load within its rated capacity close to the mast.

• It was required to slew the crane & manoeuvre the load along the jib such that the load was very close to the maximum permitted at the required radius

• During final positioning of the load it “ran away” down the jib, overloading the crane and causing it to fail at the mast section





• Prior to the accident the hook block saddle was stationary in position along the jib and under control of the mechanical saddle travel motor brake




• Under these conditions the crane was leaning forwards

• The crane controls were operated to bring the load in towards the mast section for final positioning of the load

• Instead of moving towards the mast the load ran away to the outer end of the jib






• The hook block saddle travel motor control system was a sophisticated modern PLC/Inverter electronic system

• The accident was attributed to settings of the control system

• When the controls were operated the hook block saddle travel motor mechanical brake was released (solenoid operated) before the electric motor had built up sufficient current to hold the load against the downward slope of the crane jib





• Since the crane was leaning forwards, the hook block and load started to move towards the outer end of the jib

• The electric braking of the motor was not sufficient to stop the load once it had gathered momentum

• The mast section suffered structural failure close to the edge of the building



• Extreme Weather

Utrecht, Holland – January 2007

Katowice, Poland – January 2007

Liverpool, UK – January 2007

UtrechtLiverpool



• Extreme Weather

• Speaks for itself really, no firm details concerning the Utrecht & Katowice accidents other than the Katowice crane reportedly “literally snapped in half”

• Common issues associated with high winds (above 72 km/hr, 20 m/s) can include:– The jibs of luffing cranes being blown backwards– Structural failure of jibs, counter jibs and mast sections– Prevention of the cranes ability to free slew or weathervane

• Slew brake left on• Advertising boards along the jib and counter jib acting as sails


SUMMARY

• Causes of tower crane accidents in other countries have common recurring themes with the UK and other industry sectors and include (in no particular order)

• Poor design

• Improper or not sufficiently thorough maintenance/inspections

• Inappropriate modifications or repairs and failure to implement these to sufficiently high standards

• Human Factors– Training/Competency– Miscommunication/Misunderstandings– Failure to follow procedures (shortcuts)– Failure to act if something is not right

Ian Simpson

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