A student saved her family's lives after noticing that their silver jewellery was turning black from toxic gas.
Lucy Toman, 22, and her parents Julia and David Toman were immediately evacuated from their home in Helmdon, Northamptonshire and rushed to hospital.
Experts later determined that the family had been breathing in air contaminated with potentially deadly hydrogen sulfide, the Mirror reports.
Mum Julia said the family had been dealing with "the smell of death" lingering throughout their house for two days.
The family initially though the pungent odour was coming from the drains and even called out pest control to check if an infestation was causing the stench.
She added: "We cleared all the drains to make sure that it wasn't a blockage and even had the oil boiler checked. We knew the smell was strongest in the garage."
Daughter Lucy, 22, who's currently working and studying, came home after a shift and noticed her silver jewellery had turned black and tarnished.
The rotting stench increased in severity before Lucy - who studied A-level chemistry - remembered an old classroom lesson.
Hydrogen sulphide is known for its severe pong of rotting eggs and can turn silver jewellery black through oxidation.
Exposure to hydrogen sulphide causes a host of terrifying symptoms which hit the victim rapidly and can kill within minutes, according to the Government's Compendium of Chemical Hazards.
High doses of the chemical - which is exposed to the body through inhalation - "may result in collapse, respiratory paralysis, cyanosis [lips turning blue], convulsions, coma, cardiac arrhythmias, and death within minutes", the compendium states.
Lower concentrations can "irritate the eyes and respiratory tract, resulting in sore throat, cough and dyspnea [shortness of breath]".
Mother Julia explained: "At this point, we knew that the gas could be toxic and called the fire service.
"They were here for around seven hours.
"There was two fire engines, two fire cars with toxic control people, two Anglian Water vans and an ambulance to check our blood oxygen levels and to do an ECG."
Despite being exposed to the highly toxic substance for 48 hours, blood tests at Horton Hospital turned up negative and they were given the all clear.
However, they couldn't return home until professionals eradicated all traces of the gas.
The Tomans have now returned and said they were grateful for their village community supporting them through the ordeal.
Julia said: "Luckily we had such an amazing support system in the village, and were able to stay with friends in the area while they waited for the all clear."
They have shared the story to raise awareness so other Brits will notice the signs of the fatal chemical.
