Following the latest inspections by Abu Dhabi Municipality, we thought it useful to address the topic of tower crane safety. Health and safety inspectors in Abu Dhabi have been on a campaign to impose strict compliance with safety regulations at site. Hundreds of building sites each month have received a visit from the government authority to help protect workers operating at dizzying heights. The inspectors assess all the slip-ups around scaffolds and tower cranes to ensure the workers are not at risk of falls or being hit by falling objects. They have also been examining resting areas on construction sites and also check whether workers are given personal protective equipment such as helmets and hard-soled, slip-resistant shoes, and face masks and gloves to prevent transmission of the coronavirus.
Working at height poses risk regardless of the equipment. However, with tower cranes, because it involves people and material working at significant height and free floating in the air on top of buildings, roads, and people – the risk is noteworthy. If we take the US as an example, 8% of the country’s workforce is in the construction industry yet, of all of the work-related deaths each year, the construction industry accounts for more than 22%. What’s more, construction workers are 71% more likely to suffer serious and life-changing injuries when compared with all employees in other industries put together. When we look at where these accidents are happening, crane accidents and falls are the leading causes of death in the industry.
Around the world, each year there are around 30 major accidents involving tower cranes causing an average of 50 deaths per year (maybe even higher as some countries are not reporting their accidents). These figures are staggering considering they can be avoided. In this article, we explore the top reasons, statistically, for tower crane accidents. We then look at the different active and reactive measures contractors can take to prevent accidents from happening.
Reasons behind tower crane accidents
Erection/Dismantle and Climbing: These factors account for 42% of tower crane accidents. The main reasons behind this is the failure to understand the load required for the mobile crane and to properly follow instructions of erection, dismantling, jacking up indicated by the manufacturer.
In Operation: 27% of accidents occur ‘in operation’, as in while the tower crane is working. Reasons driving this are lack of proper maintenance causing mechanical or electrical malfunctions, structural failures.
Operator Error: 13% of accidents occur due to an error by the tower crane operator. In many countries like in UK or South Korea, the tower crane operator is certified just like you would any engineer. A lot of training and assessment goes into allowing operators to be on site. When accidents happen due to operator mistake, the primary assumption is that the operator did not receive proper, up to date certification or training. Other reasons could be bad visibility from weather or for not respecting the manufacturer’s instructions or tampering with safety limits. This is why it is essential for tower crane operators to be trained and certified. The tower crane operators ideally would need to be trained enough to do daily checks for preventive maintenance.
‘Mother Nature’: 10% of tower crane accidents are caused by earthquakes and wind. Wind is probably the biggest enemy of tower cranes. It is noteworthy however that some of the accidents from wind might be due to the operator not properly shutting down the crane. Wind is the most important element to consider followed by soil. This is why each tower crane configuration will depend on the wind level of the country in which it is operating in. For Potain for example, we have catalogues based on the Wind Codes that follow that FEM, C25, D25, C50, D50, E50, among others. Depending on the country’s wind code, the tower crane configuration will change.
Because of the importance of wind, NFT has a Technical Design department specialized in studying every project based on wind, load and soil bearing capacity with tower crane configuration and location. Proper planning and wind code knowledge is key to choosing the right machine in the right configuration.
Wind is more important to be considered during ‘Crane out of service’ than during operation. Indeed, sites surroundings have a strong influence on wind behavior. Special studies are required in some cases by third parties and contractors/suppliers need to follow new wind code regulations at all times.
Important: the wind speed indicated during installation/dismantling or jacking up (around 50 KM/H depending on the country), should be less than the wind speed allowed during service (around 72 KM/H depending on the country)- however this is just the mean wind speed and can be exceeding in gusts. The surface area of loads exposed to wind is considered as less than or equal to 1 sq. m/t. If this value is exceeded, the service or ”operating” wind speed should be restricted to less than 72 km/h.
OUT OF SERVICE THE CRANE HAS TO ALWAYS BE IN WEATHERVANNING POSITIONS
Unknown: 8% of accidents reported between 2000 and 2009 had unknown causes. They fall into this category either because there isn’t enough information.
Close calls: Unfortunately, it is common to see unsafe tower crane practices and close calls. If you ask someone who has been working in this industry for a number of decades they will tell you that things are the same as they always have been.
Tower cranes do not have complexities in their design. They are basic in principle and their operating principles and erection procedures have not changed very much at all in the last 30 years. Despite this, there still continues to be tower crane accidents but it has to be said that a lot of these are completely avoidable.
Accident Example New York City, 2012
In 2012, a tower crane at the World Trade Center sent its load crashing down from 40 stores high. Thankfully it crashed back down onto the truck that it had just been hoisted from and there were no reported injuries. The load being carried weighed 40,000 pounds (18,000 kg). This type of crane can hoist up to 18,000 kg on a single-line pull and can move 190 meters each minute. So what was the reason why this crane shed its load in such a dramatic way?
In October 2011, it was reported that there was a rope that was rubbing at a bolt. When simple rubbing occurs, it doesn’t mean anything needs to be replaced. If an individual wire is flattened to two-thirds its original diameter, we can consider the wire to be broken. Crown breaks would also be determined as broken so this would have been sorted out. It leads us to ask if the company that replaced the cable didn’t deal with the cause of the rubbing. But we must also presume that the crane had been inspected after this point too and so it would have been spotted. Could the wrong rope have been installed? Load lines for tower cranes are designed at a ratio of 5:1, which means that if you have an 18,000 kg capacity on a line pull, you would need a rope that 91,000 kg capacity. The reasons aren’t clear but what is certain is that you should never miss a daily crane inspection!
Measures to be taken to Prevent Tower Crane Accidents
Tower crane accidents are rarely minor occurrences. When a tower crane comes crashing down, there are serious consequences for all involved. That said, there are many things you can do to help prevent tower crane accidents. As described , The vast majority of tower crane accidents are down to human error. The technology of tower cranes is pretty much the same as it was decades ago yet they are still a huge cause of fatalities in the workplace. However, there are several measures that can be put into place to make working with tower cranes much safer.
Preventive Measures
Before using any crane, it should be inspected thoroughly by a qualified person. Training the tower crane operator to do daily maintenance checks is extremely beneficial and efficient.
The structure itself must have a more thorough inspection regularly to determine whether it has worn-out ropes, faulty wiring, a crack or any damaged part that could lead to an accident. If it is noticed that something is damaged, the modification or repair must be done by a tower crane technician that has the qualifications and experience.
The foundation is an integral part of the tower crane as it is what holds the crane steady. It’s important that the tower crane’s foundation and structural supports are designed by either a professional structural engineer, specialized in foundation design. At NFT we always encourage contractors to have the foundation designed for an expert who will follow the manufacturer’s manual and recommendations and design based on reactions provided by the manufacturer. If there is concrete in the foundation for fixing angle, the design of the concrete needs to be done by an expert and is the sole responsibility of the contractor.
During Operations
When more than one tower crane are working simultaneously, it is important to add anti-collision or to study the location and configuration of these cranes to avoid collision. In general, the location of the tower cranes not only depends on the radius coverage and construction plan, but also the location vis-à-vis the site: example cranes must be at least 3 meters (10 ft) away from any electrical cables.
In terms of load, the crane should not carry more than it is designed for. The operator should make sure the safety device on the crane is functioning properly.
Load setting should be carried out by a rigger who has the necessary qualifications and experience. Many accidents happen because of lack of proper communication between rigger and operator. Contractors should ensure that these two parties are interdependently working together.
Regular Maintenance
Poor maintenance inevitably leads to mechanical failures. Many accidents could be prevented with proper preventive maintenance. Indeed, absence or poor maintenance will lead to:
- Lower productivity
- Uncontrolled movements
- Risk on Safety of the operators (crane drivers, fitters, technician)
- Fall of the load
- Fall of the Crane
When doing preventive maintenance, the specialized tower crane technician needs to check for:
Control : Aspect, corrosion, wear, deformation, excessive play of assembly, noise, vibrations, presence of filings, lack of lubrication, electric insulation, connections, cabling, watertightness.
Measures : Dimension of the borings of the assemblies by axes, state of rolling way, dimension of the axes, play of the axes of articulation, play of the mechanical assemblies, the dimension of axles and coupling, analysis of lubricants …
Criteria: State, deformation, out of quotation, excessive play, insufficient thickness, unsatisfactory functioning …
Recommendation : Repair, restoration or replacement of the defective components…
Avoid counterfeit parts
When choosing a tower crane or a tower crane part, brand quality is key. Many contractors opt for cheap / quick options in order to save time and money. However by doing so they are putting their site and their people at risk. This tunnel vision focuses on short term gains but in the long run, counterfeit parts will bring huge risk with very little gain! We recommend working with dealers who provided genuine parts from the manufacturer.
As a general note, when making a purchase – Don’t forget:
- The choice of a reputable brand
- Tower crane set up and commissioning
- Tower Crane operation and usage
- Planning and study of all macro and micro factors
- Maintenance
- OEM spare parts
- Brand awareness and resale value
- Training and education
- Price is not the only determinant for ROI
Proper training
Proper and continuous training for all those working around tower cranes will minimize human error. Contractors will benefit from making sure their teams are up to date with the latest certifications – investing in your people will reap benefits beyond any cost.
The Safety First! Campaign from November 2017 until Spring 2019 allowed NFT and Potain to go around client sites of NFT in the UAE, KSA and Kuwait, that have a large volume of tower cranes to raise awareness on safety practices. This was an initiative that NFT and Potain took on without any cost implications on clients because it was important to ensure that the basics of safety around tower cranes were applied. The Safety First! Campaign allowed NFT’s QHSE, Operations Managers and Potain’s top management to have direct and on the ground interaction with all those involved with the tower cranes. During the twenty-minute induction on how to work safely on Potain Tower Cranes, operator, riggers and supervisors learn the importance of daily checks, proper communication, wind effect as well as load handling; they also learn what to do during extreme weather conditions, the start and end of a shift, how to conduct basic maintenance checks and how to solve basic breakdowns. Each person was handed a bag with basic PPE and Potain’s Tower Crane safety booklet that is translated into five languages: Urdu, Hindi, Arabia, Turkish and English.
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Sources:
http://towercranesupport.com/09article.php
https://www.windcrane.com/blog/construction/wind-speed-turbulence-intensity-cranes
https://english.alarabiya.net/en/variety/2015/09/13/Crane-accidents-from-around-the-world.html
http://towercranesupport.com/09article.php
http://towercraneaccidents.blogspot.com/
https://www.thenational.ae/uae/government/on-patrol-with-abu-dhabi-s-skyscraper-inspectors-1.1084510