WorkSafe New Zealand has decided not to lay charges following an investigation into the management of asbestos in the Canterbury rebuild.

The safety regulator has been investigating cases of EQC and Fletchers workers being exposed to the substance as part of the Canterbury Home Repair Programme.

WorkSafe CEO Gordon MacDonald says, while it's obvious there were some issues early on, there was never a major threat of harm to workers and residents.

He says the biggest issue was with workers failing to properly test for the presence of the deadly material.