All cranes have capacities to help the operators understand how large of a load they can lift. The rated capacity, however, is not always constant. As the crane’s lift configuration changes, so does its rated capacity (also known as the load capacity). So, even if a crane has a standard rated capacity at one level, you may not always be able to lift loads of the maximum weight. Many times, rated capacity issues cause crane tipping or other stability problems, so if you are operating a crane while at work, make sure you understand capacity issues you might face.
As reported here, the Construction Safety Association of Ontario defines a “critical lift” as any crane lift where the load weight is over 75% of the rated capacity with the crane. In the United States, standards are similar. These are the lifts where the rated capacity comes into play.
Keep in mind that both the crane and the hoist line have a rated capacity. So, although your crane’s rated capacity might be high enough to handle the load, the wire might not. This can lead to instability, limit switch failure, and boom collapse. If the wire snaps, not only will the load fall, potentially harming those on the group, but the wire can also whip around and fly into someone, causing decapitation, internal injuries, and more. In short, this is a very dangerous situation, so you have to make sure that you read capacity ratings for both the crane and the hoist line.
The NIOSH (National Institute for Occupational Safety and Health), a division of the Centers for Disease Control and Prevention, has released a report (available here) that talks about ways to prevent mobile crane accidents. One of the issues this report covers in depth is how to safely lift loads that approach the rated capacity. As this is where load capacity matters most, the operator should always be extremely knowledgeable about the crane’s load chart. By using a load chart, you can safely make critical lifts without rated capacity problems.
Here is where employee training matters most. OSHA (the U.S. Department of Labor’s Occupational Safety and Health Administration) has clear regulations on crane lifts, and these general requirements are summed up online here. In regards to capacity, one of the most important regulations is that the crane cannot be changed unless the tags and other information are also changed. Modifying a crane can be dangerous because the load capacity changes significantly.
Regardless of modification, good employee training is essential. Always review the training manual that comes with the crane, as well as participate in on the job training that is hands-on in nature. When critical lifts are necessary, it is important to have experienced people on a team creating a plan to make sure that the rated capacity and other issues to not lead to accidents, injuries, and even deaths. Cranes are difficult to run, but in many cases, accidents are fully preventable. If you have to run a crane as part of your job, make sure you understand rated capacity issues, and talk to your employer or a crane accident lawyer about further training that can make your job safer.