Anti Two Blocking - A Life Saving Feature

Anti Two Blocking - A Life Saving Feature

In 2012 a worker was injured when the load line on an articulating boom crane broke and the crane’s load fell about 20 feet to the ground. The load line broke because the crane "two-blocked", that is to say the hook block and its stationary upper block, known as the tip sheave, came into contact. This contact puts a tremendous amount of stress on the load line and usually results in the load line breaking.

What causes the phenomena of two-blocking?

Two-blocking can happen for various reasons. In the aforementioned incident, the crane was fitted with a winch on the underside of its boom. The crane operator extended the boom to place the load, but did not spool the load line off the winch’s drum at the same time. This caused the crane’s hook block to rise and contact the tip sheave. When the crane operator continued to extend the boom after this two-blocking occurred, the load line broke. The crane lacked an anti two-blocking feature, which would have stopped this from happening. An anti two-blocking feature stalls whatever action the crane is performing so that the load applied by those actions doesn’t damage the crane’s machinery or load line.

Methods to prevent two-blocking

1. Adopt safer practices: Management should ensure that all the cranes are tested, maintained, inspected and repaired, according to the manufacturer’s instructions, the Occupational Safety and Health Administration’s standards. Also, all the articulating boom cranes should be equipped with a winch which is also outfitted with a feature to prevent two-blocking from happening.
2. Educating the workers: Ensure that workers are familiar with the manufacturer’s manual or an engineer’s instructions for the cranes they operate. There should also be

written safe work procedures for rigging and lifting loads which the management should strive to enforce. E.g., (i) advise workers not to stand or walk under loads. (ii) avert passing loads over workers and (iii) if passing a load over workers can’t be avoided, warn the workers of the danger before moving the load.

Also, management should provide employees with the information, training, and supervision necessary to ensure their health and safety when working with or around cranes.

1. When making a lift, sufficient boom length is necessary to accommodate both the boom angle and sufficient space for rigging, such as slings, spreader bars, and straps. To avoid bringing the hook and the ball into contact with the boom tip, a boom length of 150% of the intended lift is required for a boom angle of 45 degrees or more.
2. Most new hydraulic cranes come equipped with anti-two-blocking systems beforehand.

Conclusion

Since nowadays almost every crane comes equipped with anti-two-blocking systems in advance crane operators can breathe a sigh of relief. With these systems in place they can prevent potentially fatal accidents and also prevent costly damage from even happening!

LSI Wireless offers the best anti-two-blocking systems to ensure safety to the workers and the cranes themselves. It is wireless up to a transmission range of 4,000 feet and fitted with potted electronics to help increase the waterproofing.

Mike bode, the founder of lsiwireless.com, a global dealer of lsi-robway™ products.