Safe Use of Mobile Cranes in Construction Sites 1

By Occupation Safety and Health DivisionMinistry of Manpower

IntroductionThere are approximately 10,000 mobilecranes being used in Singapore. Themajority of these cranes are used in theconstruction industry to increase theproductivity of the building construction.However the misuse, failure to followsafe practices and procedures orcomplacency often led to accidents.Such accidents could have acatastrophic impact to the safety ofworkers and members of public.

This safety circular is meant to provideguidelines for the safe use of mobilecranes in construction sites.

Accident StatisticsIn year 2000, there were a total of 32incidents involving mobile cranes, ofwhich 2 cases resulted in fatalities and16 cases resulted in varying degrees ofinjury. Another 14 cases involveddamages to properties.

Causes of Crane Accidents

The main causes of accidents that hadbeen identified can be traced to thefollowing:

a) Lack of planning and supervision;b) Incorrect siting or setup of cranes;c) Failure to correctly calculate or

estimate the load;d) Failure of personnel to carry out the

correct procedures;e) Careless & Complacent;f) Use of wrong lifting gears;g) Faulty devices or machines;h) Lack of proper maintenance.

Selecting the craneCranes should always be selected tohandle the maximum anticipated loadwith capacity to spare. Otherconsideration for the selection of thecranes are the nature of lift, groundcondition, site constraints, etc.

0

4

8

12

16

Resulted indeath ofworker

Resulted inInjury toworkers

Resulted indamages toproperties

only

No. of accidents involving mobile cranes in year 2000

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Accident Case 1: August 2000

The boom of a crawler crane flippedbackwards when the steel casing (forbore piling operation) it was lifting brokeat the tip where it was shackled. Theboom and the hook block landed on theexpressway and hit a vehicle.

Safe Use of Mobile Cranes in Construction Sites 2

The crane operatorThe crane shall only be operated by atrained and competent operator. Theoperator must also be registered withthe Chief Inspector of Factories.

Documents for the craneWhen the crane arrives on site, thefollowing documents should come alongwith the crane for inspection and reviewwhen requested:

a) A valid Certificate of Test / ThoroughVisual Examination of LiftingEquipment for the mobile crane (LMCertificate);

b) Valid Certificates of Test / ThoroughVisual Examination of LiftingEquipment for all lifting gears thatcomes with the crane;

c) The log-book or log sheet for therecording of the operational testscarried out by the operator before thestart of every workshift;

If the operator is unable to produce theabove documents, the crane suppliershould be contacted and the documentsobtained before the machine is put intouse. It is advisable to state that theproduction of these documents will berequired when the crane is hired.

Siting of CraneThe stability of the crane dependsheavily on the proper siting and settingof the crane. Unless stated by themanufacturer, the crane should have itsoutriggers fully extended with thewheels off the ground. The ground

should be level andcapable of supportingthe full weight of thecrane and its load. Inaddition, sufficient andsuitable packing in theform of steel plates or

timber mats should be placed under theoutriggers to evenly distribute theweight.

The crane should also be positioned sothat:

a) The operator has a clear view ofthe operation as far as practicable;

b) There is sufficient operating space;

c) It is well away from edges ofexcavation and fixed structureswhich people may be trapped bythe moving parts such ascounterweights, etc

Planning and SupervisionAll lifting operation should be properlyplanned by a competent person beforethe actual execution and not left solelyto the crane operator.

Investigation into crane accidentsrevealed that one of the root causes ofthese accidents was due to lack ofproper planning and supervision. This isparticularly so for simple routine lifts.Hence, all contractors are advised not tobe complacent during any liftingoperation, and to plan and supervise theoperation carefully.

Site constraints that would have animpact on the safe operation of thelifting should be considered before theexecution of the lift. Examples of suchconstraints are:

a) Lifting next to or over anexcavation pit;

b) Materials or machines placedalong the access way therebyreducing the available space toextend the outriggers;

c) Site is located nearby busy traffic,or existing building or structures.

Safe Use of Mobile Cranes in Construction Sites 3

Careful planning is especially critical fprdifficult lifts such as pick and carryoperations, tandem lifting and tilt-upoperation.

“The change in radius caused bybooming down and/or telescoping outshall be considered when determining

the lifting capacity of the crane. Thereduction in the boom angle, caused bythe load when just lifted off the ground,and the consequential increase in the

radius shall also be considered indetermining the safety of a lift.”

– SS CP 37: Safe Use of Mobile Cranes

Special consideration should be givenwhen the load is required to be placedat a distant further away from the cranethan when it is being picked up, i.e. anincrease in the crane’s working radius.

PersonnelThe Factories (Operation of Cranes)Regulations 1998 requires theappointment of the following personnelfor all mobile crane operation:

• Trained lifting supervisor;• Trained riggers; and• Trained signalman.

All contractors are advised to familiarisethemselves with the duties of theseappointees as spelt out in the regulationand ensure that the only trained andcompetent personnel are appointed.

In the case where the lifting operation isout of the view of the operator (such aslifting a load from the rooftop of abuilding), the occupier is obligated toappoint sufficient number of signalmanfor the operation.

The LoadThe weight of the load should always beknown from specifications or throughcalculations. It is important to note thatthe safe working loads (SWL) indicatedin most load capacity charts are grossSWL. This means that the weight of thehook block, and all lifting gears usedmust be deducted from this gross SWLto obtain the net SWL that the crane isable to lift at that configuration.

Load Radius IndicatorThe mandatory load radius indicatorgives the safe working load at theconfiguration that the crane has beenset, and gives a warning signal whenthe radius is unsafe. The indicator:

• must be calibrated regularly;• must be configured for both main and

auxiliary hooks (when both hooks areused)

• The operator must be trained to use /set the indicator correctly to tally withthe actual configuration adopted;

It is important to note that the loadradius indicator served primarily as anoperational aid. Although the indicatorcan warn the operator of an impendingoverload, it should not be used as theonly tool to test the stability limit of thecrane during operations.

Fatal Accident Case 2: August 2000

The crane operator lifted and placed apallet of bricks onto a work platform onthe 5th storey without being instructed orsignaled to do so. The platformcollapsed together with a worker. Theworker died subsequently

The deceasedand the

platform fellfrom the 5 th

storey to theground.

Safe Use of Mobile Cranes in Construction Sites 4

Supervisors and foreman are advisednot to rely on the operator to use theindicator to determine the weight of theload. They should instead have priorknowledge of the weight of the load.This is especially critical when the liftingoperation involves the dismantling ofmachinery or structure from heights.

Singapore Standards Code ofPractice 37: Safe Use of MobileCranes: 2000The Factories (Singapore Standardsand Code of Practice) Order 2001 hasgazetted the SS CP 37 as a mandatorycode for compliance by any user. Thecode provides comprehensiverequirements on the application, safeoperation, maintenance and testing ofmobile cranes.

The guidelines and requirement laid outin this circular are extracted from thecode.The crane's safe working load is alwaysindicated for freely suspended loads. It isexpressly forbidden to use the crane to dragany load, or any operation that may cause thehoist line to be out of plumb.

Slewing should be done slowly to maintaincontrol of the load.

Tag lines should be used where applicable tominimise swing

The operator should stay at the controls at alltime when the loads are suspended.

Interpolation of the safe working load in theload capacity is disallowed unless specificallyallowed by the manufacturer. Extrapolation isstrictly disallowed.

No additional counterweight shall be added tothe crane unless specifically allowed by themanufacturer.

All contractors are advised to familiarisethemselves with the requirementstipulated in the code.

Checks and MaintenanceThe crane should be in good workingcondition when it arrives on site andbefore the start of the workshift. Inaddition to the statutory annualinspection, the manufacturer’srecommendation on the inspection andmaintenance regime should also befollowed closely.

Types Checks

FunctionalChecks

• Check limit switches e.g.over-derricking; overhoisting

• Slewing• Telescoping• Travelling• Safety devices

IntegrityChecks

• Wire ropes• Rope terminations• Hook block• Boom section• Rope pulleys• Rope guards

The checks listed in this table are not exhaustive.

Issued byTHE CHIEF INSPECTOR OF FACTORIES

MINISTRY OF MANPOWER

Accident Case 3: June 2000

The crane operator had lowered his hookblock from an opening into the basementinfrastructure. The workers at thebasement then pulled the hook blockaway from the opening and rigged up atruss structure. They then gave thesignal to the operator to lift. The boom ofthe crane snapped when the load wasdragged out.

Dragging is expressively forbidden

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