Last year, a crawler crane accident in high winds killed 109 people in Mecca. In February, a collapse as a crane was being lowered in rising winds, killed one person and in Tribeca, New York.

The first accident happened on the afternoon of September 11, when a storm suddenly picked up over Islam’s holiest city, leading to the collapse of a Liebherr LR 11350.

This crawler crane fell into the Grand Mosque with the hook block snapping off and crashing into the crowds.

The LR 11350, owned by Saudi Bin Ladin Group, was used to extend access to the site for increasing numbers of people to Hajj, the annual pilgrimage.

Liebherr released its reports, saying that wind speeds were far higher than the crane’s safe operating wind speed of 9m/s. CNN reported winds reached 22m/s, while Liebherr’s own data, from a tower crane anemometer at the site, showed wind speeds reaching 29m/s. These reports were carried out by computer simulations conducted locally, by the accident inquiry and by satellite data from NASA.

In order to investigate the accident, Prince Khalid Al-Faisal Al Saud, governor of Mecca, formed a committee, which examined the correspondence between engineers and operating technicians, saying that the position of the crane at the time of the crash was “inappropriate”.

An official statement from Liebherr confirmed that “The crawler crane could not withstand such a high wind load and that the boom should have been lowered to the ground preventatively to avoid the tilting of the crawler crane.”

Instead, the crane’s 102m main boom+84m luffing jib had been left at an 85° boom angle, ready to resume work after the annual Hajj season.

Local Saudi papers, including Al- Watan and Khaleej Times, reported in February that some 40 people will stand trial before three courts in Jeddah for their role in the incident.

The second accident occurred on 5 February, while the crew operating a crawler crane in Lower Manhattan began to bring down the boom, which stretched 565ft toward the sky.

The workers needed to lower the Liebherr LR 1300 to a secure level as wind gusts neared 25 mph, in addition to the falling snow.

Instead of having a controlled descent, the crane began to fell suddenly before crashing onto Worth Street, killing a man walking in Tribeca.

The crawler crane was being used to install generators and air conditioning units at the top of 60 Hudson Street and it was inspected by the Buildings Department to approve an extension to its present length, officials said.

The Bay crane, operated by Galasso Trucking and Rigging, was rated to withstand wind gusts of up to 25 miles per hour.

The Police Department and the Buildings Department opened investigations last February and they are focusing on the wind and the height of the crane, as well as the company operating the vehicle.

Following this accident, New York City mayor Bill De Blasio introduced a new task force to estimate crane safety standards.

New safety policies include restrictions on crawler cranes such as sidewalk protections and notification procedures.

The new restrictions on crawler cranes orders that they “must cease operation and go into safety mode whenever steady winds are forecast to exceed 20 miles an hour or gusts are forecast to exceed 30 miles per hour,” said de Blasio.

The NYC Department of Building is raising the base penalty for failure to safeguard cranes from $4,800 to $10,000.

Another crane accident happened last February in Louisville on the East End Bridge project. Wind gusts ranged from 40-50 mph when the crane toppled over at the construction site near the Ohio River, again calling safety into question.

Education
Christoph Kleiner, managing director at Liebherr, says: “It’s important to educate crane owners to work safely in high wind conditions in order to avoid such disastrous accidents.

“First of all, crane owners need to monitor the weather forecast, checking the maximum wind speed allowed for load chart.”

“If they are exceeding the maximum allowed wind speeds for the operation, they need to go into a parking position. Prior to the arrival of strong wind, crane owners should prepare the construction site, planning a safe parking position. If this is not possible, they need to lower the crane and to wait for better weather conditions.

“Otherwise we recommend alerting the manufacturers to support for special cases. For example, in the Mecca accident there was plenty of space to take the boom down, but they didn’t use it.”

Ryusuke Yanagido, marketing manager for larger crawler cranes at Kobelco agrees: “I strongly recommend checking weather conditions.

“Using an anemometer is relevant, but it depends where it’s positioned to record the wind speed. It’s better to put the anemometer at the top of the crane or in the highest possible position.”

Another system to monitor high wind speeds is the KCross, which represents a crane remote observation satellite system.

“The Kcross allows the customers to log in to the system, accessing to data on machine’s operational status and operating location. By using this data for maintenance and crane operation planning, cranes may be utilized more efficiently,” says Yanagido.

“Specifically, the system allows to monitor wind velocity, but this is possible for the machines fitted with wind speed gauge only.”

Soren Jansen, general secretary of the European Association of abnormal road transport and mobile cranes (ESTA) suggests determining a contingency plan to bring the crane into a safe position in case of emergency.

This plan should also include sufficient space to carry the equipment in a safe position.

“With regards to the Mecca accident, the wind surface of the boom was 80sqm at the height of 140- 150m and obviously, the wind posed immense pressure on the crane,” says Jansen.

“Nowadays boom lengths are so long and such height represent a commonplace. Of course the bigger it gets, the more careful you have to be, the more planning you have to do.”

The International Crane Stakeholder association (ICSA) provides a guidance document, Leaving mobile cranes unattended in (partially) erected mode.

This guidance has been reviewed and jointly adopted by seven members: Association of Equipment Manufacturers (AEM), Crane Industry Council of Australia (CICA), The European Association of abnormal road transport and mobile cranes (ESTA), European Federation of Material Handling (FEM), Specialized Carriers & Rigging Association (SC&RA), China Construction Machinery Association (CCMA) and Japanese Construction Equipment Manufacturers Association (CEMA).

ICSA gives specific instructions for crawler cranes with lattice boom, “If the predicted wind speed exceeds the maximum permissible value for the selected configuration as given in the operator’s manual, the boom shall be lowered to the ground before the maximum wind speed allowed during assembly and disassembly has been reached”.

In order to predict the risk of high winds, the FEM recommends crane owners not just checking the weather forecast, but also the gusts and elevation-related wind gusts.

Forecasts will only give average wind speeds at ground level. To accurately assess the risk to tall crawler cranes, these should be multiplied to account for both gusting and for higher wind speeds at elevation.

According to Stuart Edwards, an Australian lift engineer with over 15 years’ experience in construction engineering and modularisation, crawler cranes must be set up on firm level ground as they not able to level themselves using outriggers.

“Compared to tower cranes, crawler cranes are not typically permitted or have the potential to weather vane. This makes assessing and considering the predicted wind conditions when the crane is not used (for example overnight) more important,” says Edwards.

“Compared to telescopic mobile cranes the boom of a lattice boom crawler crane can not be easily retracted. This makes it necessary to lay down and/or lash the boom for high wind events. This is not relevant for telescopic boom crawler cranes where the boom can be retracted.”

“Most manufacturers specify a wind speed limit for lifting activities.

The main figure stated is the load chart wind speed, which may vary depending on crane configuration.

Higher wind speeds may be permitted if the percentage of the chart lifting capacity is reduced. The load chart wind speed must also be reduced to a permissible lifting wind speed depending on the surface area of the load,” says Edwards.

Prior to the permissible lifting wind speed being exceeded the load should be safely lowered to the ground, stopping the lifting operations, as well.

“Once the permissible lifting wind speed is exceeded many manufacturers specify a wind speed limit where the boom may still be raised but placed in a parked position.

This parked position usually requires the crane to be in a particular configuration or boom angle. If the manufacturer does not specify a parked position the crane boom must be lowered to the ground,” Edwards says.

“Once the limit for the parked position is exceeded most manufacturers specify that the boom must be lowered to the ground. The lowering process should be conducted sufficiently prior to a high-speed wind event and in accordance with the lowering procedure.

“Depending on the crane configuration and manufacturer requirements this may require the crane being slewed at a certain angle to the tracks, using blocked crawlers, using wheels on the luffing boom tip, attaching outriggers or using an assist crane to lower the boom.”

Edwards says that the crane owner should lower the boom onto a suitable level pad, which can withstand the load from the boom and supports the boom at the points.

“Lashing at the boom tip or boom base may be required. In extreme weather events the boom may need to be removed from the crane and lashed separately to the crane due to the potential to impart loads to the crane superstructure.

“Lower limits than the technical specifications may be appropriate based on the experience of relevant personnel.”

What’s more, the monitoring should ideally be conducted at a height near the boom tip, identifying a hierarchy of who is responsible for monitoring current wind speeds and forecast winds speeds should be agreed on site.

“For example, the crane operator may be responsible for monitoring wind speeds during lifting operations and the foreman may be responsible to assess the forecast overnight or over an extended break.

“Most crawler cranes are fitted with a wind speed meter and the cost of retrofitting onto an existing crane is usually reasonable. Certain regulators mandate that wind speed meters must be fitted. The crane wind speed meter can be connected to a remote monitoring system if desired and may be beneficial.

“Project based weather monitoring stations are useful for larger projects. They can be set up to be accessed from anywhere and send notification alarms to mobile phones. Government weather bureaus provide a wealth of information, forecasts and alerts, but third party information sources such as specialised forecasters can be used.”

Pierre da Villiers, Global HSQE Manager for ALE Company, emphasized the importance of being proactive to elevate any reactive actions through planning and setting contingencies.

“We utilise accurately tested measuring devices to get correct readings. However, we are realistic and as we are faced with unexpected changes, we would always ensure that an emergency procedure is in place. This would involve safely lowering the boom and load to a secure position.

“Training and developing our operators is one of our priorities; our experienced teams are assessed internally on their competency and undergo practice operations to ensure they are fully trained with the knowledge of how to react.”

At ALE they have industry experts in the global crane division and technical directors, says da Villiers, adding that these crane experts are updated regularly with information from manufacturers and industry specialists. Thus, they can learn further from the industry collectively and bring into our own practices.

“Similarly, we actively participate in the Industry Risk Committee, sharing best practice to further protect our people, environment and assets,” says da Villiers.