SAFE USE OF MOBILE CRANES

Author:Mihajlo StuparHSE Manager

PRO Lifting Solutions LtdRepublic of Serbia

February 2016.

● Mobile cranes are indispensable assistants in lifting heavy loads in the industry. They are primarily used for lifting, lowering and transporting loads.

● Mobile cranes moved loads horizontally by swinging or traveling. Most of them consist of a carrier and superstructure equipped with a boom, jib (optional) and hook.

● There are mechanical and hydraulic types of mobile cranes.

● Mechanical mobile cranes are also referred to as "conventional" crane and they have greater capacity.

● Hydraulic cranes have greater mobility and require less setup time.

BASIC DEFINITIONS

● Crane – consist of a rotating structure for lifting and lowering horizontally structure on rubber tires or crawler treads.

● Hoist – used to lift and lower load.

● Boom – an inclined spar, strut, or other long member supporting the hoisting tackle.

● Boom stops – a device used to limit the angle of the boom at its highest position.

● Brake – to slow or stop motion by friction or power.

● Block – sheaves or grooved pulleys in a frame with hook, eye and strap.

● Jib – extension attached to the boom point to provide added boom lenght for lifting specified loads.

● Radius – horizontal distance from center of rotation to the hook.

CRANE CAPACITY● Crane capacity is controlled by its operating radius.

● Capacity depends on: position of boom with respect to the carrier (over the front or over the rear or sides), amount and configuration of the counterweight.

● Crane manufacturers provide lifting data that includes: range diagram, load rating charts, PCSA rating class, miscellaneous notes and dimensions.

● Safety regulations limit maximum crane load to a percentage of the tipping load (load that will cause the crane to actually begin to tip).

● Notice that hook blocks, slings, spreader bars, and other load-handling devices are considered part of the load and their weight must be included in the maximum safe load capacity calculation.

● Electronic load indicators are available that measure the actual load on the crane and provide a warning if the safe capacity is being exceed.

● Lifting capacities are based on ≤ 85 % of tipping load on outriggers and on ≤ 75 % of tipping load on crawlers.

● A standard method of rating the capacity of mobile cranes has been adopted by The PCSA Bureau of The Construction Industry Manufactures Association (CIMA).

● The key to lifting a maximum capacity load is the outriggers. They provide a solid platform for the crane safety operations. Statistic show that at least 50 % of crane incidents occur because crane or outriggers are not set-up properly.

LIEBHERR LTM 11200-9.1 – ONE OF THE BIGGEST MOBILE CRANE IN THE WORLD

● Lifting capacities:

● 1200 t on 2.5 m radius – with heavy lift boom and additional equipment.

● 140 t on 20 m radius, 33.5 t on 50 m radius, etc.

TEREX CC 8800-1 – ONE OF THE BIGGEST CRAWLER CRANE IN THE WORLD

● Lifting capacities:

● 1558 t on 10 m radius, 873 t on 30 m radius, 334.5 t on 60 m radius, etc.

● Crawler crane can move with load. Ofcourse, for this operation you must have very good ground conditions.

RESPONSIBILITIES, CONDITONS

● Have the right crane for the job.

● Assure operator is adequately trained.

● Assure riggers are competent.

● Ensure crane is in safe operating condition.

● Know the weight of the load.

● Know where the center of gravity is.

RESPONSIBILITIES, CONDITONS● Know the rated capacities of rigging.

● Reduce capacities as sling angles increase.

● Know how hitches affect sling capacities.

● Use proper sling sets for the load.

● Protect slings from sharp surfaces.

● Test lift uneven loads for balance.

● Inspect all slings, chains, hooks, etc.

● Stay clear of raised loads.

RESPONSIBILITIES, CONDITONS● Provide overhead protection for other workers.

● Provide proper working area.

● Maintain clearance with overhead power lines.

● Assure adequate ground stability – as load leverage increases, pressure increases nearest the load.

EQUIPMENT FOR BINDING● Slings are rated for vertical hitch.

● Chocker hitches can reduce capacities by half.

● Basket hitches can increase capacity by 2 for straight vertical basket.

● If sling / chain angles are too shallow, the slings / chains could slip.

● Shallow angles also can over stress slings / chains.

Chocker Basket

EQUIPMENT FOR BINDING● Slings / chains must be inspected before

each use. They should have tags that indicates capacities.

● Slings are safer then chains, because on slings you can see initial damage much easier.

● Immediately remove damaged or defective slings from service!!!

TENSION IN A SLING LEG

T – tension in a single leg.

WL – weight of load.

N – number of sling legs.

L – lenght of sling leg.

V – vertical distance between hook and load.

● The sling stress is proportional to the angle of the sling.

SLING ANGLE AND CAPACITY

87 % 70 % 50 %

● Rated capacities must be reduced as sling ahgle increases.

● Slings should be set at a minimum of 60 degree angle.

CAUSES OF CRANE ACCIDENTS

● The main causes of crane accidents are:

● lack of planing and supervision,

● incorrect siting or setup cranes,

● failure to cerrectly calculate or estimate the load,

● failure of personel to carry out the correct procedures,

● use of wrong liftinting gears,

● lack of proper maintenance,

● careless and complacent,

● faulty device or machines.

SELECTING THE CRANE● Cranes should always be selected to

handle the maximum anticipated load with capacity to spare.

● Other consideration for the selection of the crane are the nature of lift, ground condition, site constraints, etc.

THE CRANE OPERATOR

● Make sure the crane operator can see the:

● Rated load capacities,

● Operating speeds,

● Special hazard warning and instruction.

● The crane shall only be operated by a trained, health and competent operator, with cooperation of trained lifting supervisor, trained riggers and trained signalman.

DOCUMENTS FOR THE CRANEWhen the crane arrives on site, the following documents should come along with the crane for inspection and review when requested:

● a vaild Certificate for the mobile crane,

● Valid certificates for all lifting gears that comes with the crane,

● The log book or log sheet for the recording of the operational tests carried out by the operator before the start of every workshift.

If the operator is unable to produce the above documents, the crane supplier should be contacted and the documents obtained before the machine is put into use. It is advisable to state that the production of these documents will be required when the crane is hired.

SITING OF CRANE● The stability of the crane depends heavily on te proper siting and setting of the crane.

● Unless stated by the manufacturer, the crane should have its outriggers fully extended with the wheels off the ground.

● The ground should be level and capable of supporting the full weight of the crane and its load.

● In addition, sufficient and suitable packing in the form of steel or plastic plates or timber mats should be placed under the outriggers to evenly distribute the weight. Surface of these plates or mats should be at least twice bigger then surface of outriggers which is above.

● The crane should also be positioned so that:

● The operator has a clear view of the operation as far as practicable,

● There is sufficient operating space,

● It is well away from edges of excavation and fixed structures which people may be trapped by the moving parts such as counterweights, etc.

● Fully extend all outriggers for maximum capacity.

Proper outrigger setup

Not recommended outrigger setup. In this situation load should be on the other side of the crane, then the maximum pressure will not be on this outrigger.

Improper outrigger setupPoor outrigger setup

No comment...

WORK NEAR POWER LINES● Who is at risk –

● Operators are normally safe if they stay in the cabin.

● Ground personnel are over 8 times more likely to be killed.

PLANNING AND SUPERVISION● All lifting operations should be properly planned by a competent person before the actual

execution and not left solely to the crane operator.

● Investigation into crane accidents revealed that one of the root causes of these accidents was due to lack of proper planning and supervision. This is particularly so for simple routine lifts. All contractors are advised not to be complacent during any lifting operation, and to plan and supervise the operation carefully.

● Site constraints that would have an impact on the safe operation of the lifting should be considered before the execution on the lift. Examples of such constraints are:

● lifting next to or over an excavation pit,

● materials or machines placed along the access way thereby reducing the available space to extend the outriggers,

● site is located nearby busy traffic, or existing building or structures.

● Careful planning is especially critical for difficult lifts such as pick up and carry operations, tandem lifting and tilt-up operation.

LOAD RADIUS INDICATOR● The mandatory load radius indicator gives the

safe working load at the configuration that the crane has been set, and gives a warning signal when the radius is unsafe.

● The indicator:

● must be calibrated regulary,

● must be configured for both main and auxiliary hooks (when both hooks are used),

● the operator must be trained to use / set the indicator correctly to tally with the actual configuration adopted.

● It is important to note that the load radius indicator served primarily as an operational aid. Although the indicator can warm the operator of an impending overload, it should not be used as the only tool to test the stability limit of the crane during operations.

CHECKS AND MAINTANCE● The crane should be in good working

condition when it arrives on site and before the start of the workshift. In addition to regulary inspections, the manufacture's recommendation on the inspection and maintance regime should also be followed closely.

BASIC RADIO COMANDS HAND SIGNALS

● Use load line.

● Use wipline.

● Boom up – boom down.

● Boom up and hold the load.

● Boom down and hold the load.

● Swing right – swing left.

● Take the load up – down with the load.

● Extend boom – retract boom.

● Etc...

In these 2 accidents nobody has died, but material damage is very high, as you can see on the pictures...

Why these accidents happened?Failure of operators to carry out the correct procedures...

T A K E C A R E , B E S A F E ;-)T A K E C A R E , B E S A F E ;-)