A registered gas fitter who brought an outdoor generator below the deck of his boat despite knowing that carbon monoxide sensors were disabled, awoke to find his partner and her 10-year-old daughter dead, a court has heard.
Matthew Eteson, 42, pleaded not guilty to manslaughter by gross negligence after jurors were told that he had fabricated an exhaust system for the petrol-driven portable generator used to power the mains appliances on the boat, moored on Lake Windermere, Cumbria.
His partner Kelly Webster, 36, and her daughter Lauren Thornton were found in their sleeping quarters on the second-hand Bayliner 285 motor cruiser Arniston with fatal levels of carbon monoxide in their bodies.
He denies the charge.
Preston Crown Court was told that Eteson, of Appleton Road, Hale, Cheshire, who was "an experienced boat owner" had fabricated the exhaust system with a silencer because it was "noisy" to fellow neighbours and had fitted it into the engine compartment.
But the court was told that it had been of "poor design" and the materials he had used were unsuitable causing the system to fall apart under the load of the heater and discharging the gases.
The family had gone to the Lake District for the Easter bank holiday weekend to celebrate a friend's birthday.
However on the afternoon of April 1 2013 Eteson removed the generator from the deck and used it to power a 1kW fan heater to heat the sleeping quarter.
The court was told that there had been no warning to the build-up of the gas because the carbon monoxide sensors had previously disabled the sensors.
For the prosecution Mr Graham Reeds QC said that the mother and daughter were found dead in the positions in which they had slept.
Eteson, who had been sleeping in a separate compartment further away from the generator also succumbed to the effects of carbon monoxide poisoning, and found the bodies.
It is not alleged that he intended any harm to come to either victim.
Mr Reeds said from Eteson's training as a Gas Safe installer in dwellings and non-dwelling he was "well aware" of the risks to human life through exposure to carbon monoxide.
He said: "Had they not been disabled they would have alerted the occupants to the build-up of carbon monoxide in the sleeping quarters. The defendant was well aware of the fact that carbon monoxide sensors fitted to his boat were not working.
"Good practice would decide against bringing an outdoor generator indoors."
In court, the defendant who was allowed to remain outside the dock, listened as he was flanked by his father.
The prosecution said it was their case that Eteson was "criminally responsible" for their deaths.
Mr Reeds added: "It was found that a copper pipe had been crudely attached to the steel exhaust outlet of the generator with self-tapping screw.
"Leading from the exhaust outlet to the silencer was a section of cooper pipework. This included a joint that had been fashioned using solder which has a relatively low melting point.
"It is very poor practice to attach metal to copper or to use solder in joints between copper pipes that will be subjected to very high temperatures."
A reconstruction of the system had collapsed after 3 minutes and 30 seconds.
The court was told that the generator had not been strapped down and the silencer had become detached from the pipe work because of joint failure.
Mr Reeds said that expert witnesses criticised Eteson's design and use of materials, with one saying that if his work had been measured against the gas industry's Unsafe Situations Procedure it could only be defined as "Immediately Dangerous".
Eteson claimed that he had tested the fabrication at home before he fitted it. The court was further told that following the deaths, he and his father carried out reconstructions of the system which had ran for over three hours without the joints failing.
But Mr Reeds said another specialist said the standard of work was of "a level not expected of an alleged qualified and competent engineer who has been in the industry for many years".
In a statement read to the court Kelly's mother Nia Webster said she had tried to text her daughter the day before her death to see if she would be back for Easter dinner but had not received a reply.
The court heard that when Mrs Webster asked Eteson if there was any carbon monoxide detectors, he said "they were not working" adding, "he said they had a portable detector but Kelly kept unplugging it when she was cooking" and it was "probably thrown in a drawer".
The case continues.