Surgical theatres closed at University Hospital of Wales
Five surgical theatres at Wales' biggest hospital are closed and 19 operations have been cancelled due to a problem with the ventilation system.
Cardiff and Vale University Health Board is investigating the issue at Cardiff's University Hospital of Wales.
Staff found black specks in a theatre, leading to 11 cancelled operations on Friday and another eight on Monday.
Surgery is continuing in other theatres and the health board said there is no evidence of a risk to patients.
Tests have been carried out but the origin of the specks is still unknown.
Director of nursing Ruth Walker said: "We hope to have it resolved shortly and will ensure that all those affected are seen as soon as possible."