New research shows rebuild workers in Christchurch are being exposed to unsafe levels of silica dust.
WorkSafe New Zealand commissioned research into handling of the dust, which is often found on construction sites.
Its departmental medical practitioner, Bill Glass. said silica causes lung disease, lung cancer and could damage kidneys.
Professor Glass said many of the workers were not even aware silica was a hazard.
He said in the risky jobs, such as concrete polishing and grinding, they found high levels of dust exposure compared with the national and international standards.
Mr Glass said the bigger firms tended to have good systems, but many smaller operators needed to improve their practices and awareness of the risk among workers.