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Understanding Two Blocking and Why Cranes Need ATB Warning Systems

ATB, short for anti-two-block, warning systems are now commonly used on cranes to avoid the incident of two blocking. However, very few people understand what exactly two blocking is and why ATB warning systems are so crucial. To get a better understanding, let’s take a closer look:


What is Two Blocking

An accident report detail from OSHA describes an incident of two blocking which took place back in 2011, which serves as a good explanation. In the incident, a permanent overhead bridge crane was being operated by a crane operator and an employee guiding them.


Crane hoist carrying a heavy load

The crane had an eighty-ton main hoist and a ten-ton auxiliary hoist. The crane’s main hoist was being used to lower a load. The crane operator briefly operated the control for the auxiliary hoist, thinking it was for the main hoist, later switching over to the main hoist control, and raising the load by several feet.


Before the crane could move the load horizontally, a loud noise was heard and the load block assembly of the auxiliary hoist separated from the load line. The incident occurred when the auxiliary hoist block came in contact with a structural component from the crane’s trolley assembly which caused the hoist wire to break.


Even though there was an upper limit switch installed on the hoist, it wasn’t tested properly before use. As a result, the auxiliary hoist block assembly fell and crashed onto the employee guiding the operator, who died from the resulting injuries.


Crane in operation

Why Cranes Need ATB Warning Systems

If this crane had an ATB warning system, such an incident could have been avoided. ATB warning systems warn the operator if and when two-blocking occurs. The system features integrated sensors to detect two blocking and is available in wired or wireless forms.


Wired ATB warning systems are recommended for fixed boon cranes and it helps ensure that the hook doesn’t come in contact with the boom tip. Wireless ATB warning systems are more compatible with telescopic and lattice boom cranes, featuring audio and visual alarms to alert the crane operator.


It’s also worth mentioning that ATB warning systems are not just used for additional safety but are deemed mandatory by OSHA for any crane operation. Installing ATB warning systems is necessary for cranes because they not just improve the safety of the operating crew but the personnel working around the crane as well.


Moreover, the device helps ensure that regulatory compliance is fulfilled and the liability is reduced as well. ATB warning systems also ensure that crane lift operations are carried out safely and without any inconveniences or downtime.


Get ATB Systems with Crane Warning Systems Atlanta

Crane Warning Systems Atlanta is the national supplier of RaycoWylie crane safety products including anti-two-block devices. We offer wired and wireless ATB Systems such as the R147 A2B or the R140 A2B. Get in touch with us now to learn more.

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