An appliance manufacturer was investigated for corporate manslaughter over the deaths of five people linked to gas cookers, an inquest heard.
Devon and Cornwall Police was looking into the deaths of five people in Cornwall in two separate incidents in 2010 and 2013, the hearing was told.
Coroner Geraint Williams heard 18 deaths in the UK and Ireland had been linked to cookers made by Beko’s Turkish parent company Arcelik.
No charges were brought.
Kevin Branton, 32, and his housemate Richard Smith, 30, were found dead in their house in Saltash, in November 2010.
An initial inquest conclusion of accidental death by the Cornwall coroner was quashed by the High Court and a new inquest was ordered after three members of the Cook family – John, Maureen and their daughter Audrey, died at their static caravan in Camborne, in February 2013.
All of the victims had been using a similar type of gas cooker and died from carbon monoxide poisoning, the inquest heard.
Det Sgt Jonathan Bray said the cookers had a rubber seal around the grill door and the “danger occurred when that grill door was shut” because that restricted airflow and caused incomplete combustion, producing dangerous levels of carbon monoxide.
He said both the Cook family and Mr Smith and Mr Branton appeared to have died after an “accidental switching on of the wrong compartment of the appliance” while trying to cook food in the oven.
Phil Poolley, from Intertek, a London-based product testing and certification company, said his company had been involved in testing the cookers, making sure they complied with British and European safety standards.
He said at the time those standards did not require gas ovens to be tested with the grill doors closed unless the manufacturer’s instructions indicated they could be used in this way.
Mr Williams asked if it was not “glaringly obvious” that someone could inadvertently close a cooker door or turn on the wrong knob.
Mr Poolley said: “It is now … in hindsight it is foreseeable because it has happened quite a lot.”
He said the standard had since been changed to ensure cookers were tested in this way.
The inquest continues.