The company which produced a cooker linked to at least five people's deaths didn't test it with the grill door closed, an inquest has heard.
Maureen Cook, 47, Audrey Cook, 86, Alfred 'John' Cook, 90, Kevin Branton, 32, and Richard Smith, 30, all died of carbon monoxide poisoning in two separate incidents.
They died in Cornwall in 2010 and 2012, and it was found they all had cookers made by Arçelik, the parent company of Beko.
During the inquest, it was heard how the cookers created a buildup of deadly carbon monoxide when the grill was used with the door closed.
A spokesperson for Arçelik said the company conducted "misuse" testing, but didn't foresee the grill being operated with the door closed because they coudln't "see into the minds of the end user".
The inquest held in Truro, Cornwall, began on Monday, November 16, and is expected to continue for seven days.
Senior coroner for Cornwall Geraint Williams read out a statement by Alp Karahasanogiu, product director at Arçelik.
In the statement, Mr Karahasanogiu said how Arçelik began designing their own products after 1994 and that testing was carried out onsite.
The statement said: "Approved products are subject to further testing and related certifications are obtained.
"The objective is to produce a product to meet customer demand that is safe and affordable.
"Product safety is the primary criteria in the design faze.
"Arçelik test the products not just in the manner directed, but also how a customer might use a product not as directed.
"Obviously this is more difficult to test for as it is not always possible to see into the minds of the end user.
"No one foresaw that the grill might be used with the grill door shut on purpose or by accident."
The inquest heard how an instruction manual for the cooker included a rule that the grill must be used with the door open.
But Mr Karahasanogiu's said this was due to the nature of the cooking process, not because the company were aware of a carbon monoxide issue.
The statement continued: "One of the main issues is the use of the customers with the door closed.
"The instruction manual provided instructions to the end users to operate the grill with the door open.
"The instruction was to do with the efficient operation of the appliance. Grilling uses a different cooking process than oven cooking.
"This is why the instruction is given to grill with the door open."
The unit in question had a rubber seal around the cooker door which created a complete seal, allowing the gasses to build up in the grill area.
Mr Karahasanogiu's statement said that he wasn't certain why the rubber seal was included as the relevant staff were no longer with the company.
The design was later changed to allow an air gap.
The statement continued: "While I cannot say for certain, the widely held opinion of my colleagues is that this would have been done for reason of product quality.
"Without the rubber surround the door would rattle and make a loud noise on closing.
"Where there is metal on metal contact we would include something to reduce noise.
"The design was later changed to a 'U' shaped rubber surround which created an air gap."
The inquest heard that Arçelik also conducted external testing to make sure their products met industry standards.
The Beko products were tested by a company named Intertek.
A spokesperson for Intertek, a Mr Poolley, will give evidence at the inquest at a later date.