There were three elements that led to the fatal CO poisoning:
- The unlawful action of installing an open flued gas appliance (water heater) in a prohibited space such as a bathroom.
- The unlawful omission of failing to provide adequate fixed ventilation in a space when installing an open flued gas appliance.
- The operation of a ventilation system that created negative pressure in an inadequately ventilated space.
These three elements led to a situation where the flame became starved of oxygen (vitiated) which led to a rapid build-up of carbon monoxide in the shower cubicle. The removal of any one of these elements may have prevented the incident.