Use of two workers to lay blocks over 20kg has been suggested in previous guidance but this has not proved to be workable and is no longer recommended. There is a risk of immediate injury or of long term physical disability from single-handed repetitive manual handling of heavy masonry units; particularly those weighing above 20kg. When designing or specifying blocks, the lightest block that fulfils the performance criteria should be chosen. In the majority of cases blocks weighing under 20kg are available that will fulfil the required design specification. It is not just the weight that matters though; a safe system of work will include suitable precautions to avoid or minimise all hazards. This includes the weight, the repetitive nature of the work, poor posture, stooping and reaching as well as the risks associated with slips/trips/falls, sharp or rough edges and skin hazards caused by contact with mortar.
[b]If you want general information on manual handling risks in construction please see [Musculoskeletal disorders](http://www.hse.gov.uk/construction/healthrisks/msd.htm).[/b]