An H-block, or double open-end unit, is a substitution material that can help reduce musculoskeletal disorders (MSDs) from lifting and carrying. The H-block is open on both ends which increases the space available for rebar and grout.
H blocks are concrete masonry units (CMU) without ends (Figure 1). Masonry contractors in the Western US use open-end blocks more frequently than other regions of the US due to seismic specifications.
Figure 1. Standard H-Block
Heavy lifting and carrying can cause low back disorders, such as muscle strain or a disc herniation (“slipped disc”), which is bulging of disc material possibly pressing on the spinal cord or nerves that go into the leg. The H-block can help reduce heavy lifting and carrying by reducing the weight of the standard block being lifted and carried in the worksite.
H-block is open on both ends which allows masons to place the blocks around vertical rebar. This innovative design eliminates the need to lift the CMU above shoulder level reducing the risk for musculoskeletal disorder of the back and shoulder.
Contractors indicate the design of H-block allows masons to work around a vertical rebar making the job easier, safer, more efficient, and with less stress for the body. Instead of lifting the CMU over the top of the rebar, masons can maneuver the block around the side of the rebar at a height that is comfortable for them.
Safety and health experts believe that masons will be less likely to develop musculoskeletal disorders of the back and shoulder if they are able to substitute regular CMU for H-block.
Lifting H-blocks around the rebar instead of above the rebar is less fatiguing and should increase productivity.
Contractors indicate that one of the drawbacks is that H-blocks break frequently due to improper shipping, storing or handling. Other contractors have mentioned that they are difficult to handle. Additionally, efficient workplace layout is important as this may help limit damage and promote load balance with could limit heavy loads.
Dan Anton, PT, PhD, ATC – Eastern Washington University, and Carlos Sanchez-Marin, DDS, MS – University of Iowa