It was a chilly autumn night in May 2010, so Vanessa Robinson left the heater of her rented home on and put her sons to bed. It was a decision she didn’t think much of at the time.
And when the Victorian mum awoke hours later to find her sons, Chase and Tyler, distressed in her room, she thought it was because one had a nightmare. The boys, six and eight years old, climbed into her bed and the family went to sleep. Only later did she find out that her family were likely already suffering the effects of the carbon monoxide slowly filling their Mooroopna home.
At 6pm the next day – almost 24 hours later – Vanessa awoke to banging on her door and the ringing of her phone. It was her ex-husband, the boys’ dad, Scott. He was meant to take them to the park that day and was worried and wanting to know what had happened.
In severe pain, "delirious" and noticing her sons' beside her weren't okay, Vanessa managed to call an ambulance. Soon after they arrived to pick her up and take her to hospital.
After a second hospital transfer to St Vincent's in Melbourne and days in an induced coma, Vanessa learned what had happened.
Her sons had suffocated in their sleep and she had suffered severe carbon monoxide poisoning. Gas had leaked from their rental property's heater and filled her home to more than 3000ppm. The safe limit is zero. If she hadn't been awoken that evening, she could have died as well.
It was shocking news to the 37-year-old. Vanessa told Mamamia she'd never been made aware of the importance of taking care with gas-fuelled appliances.
"It was really difficult to wrap my head around that fact because I grew up with gas heaters and never were we warned about the dangers."
Since then, she's been doing all she can to ensure this never happens to another family again.
"This is the one huge issue that many Australians face that we have no knowledge about," she said.
"Especially for parents. Before you have a baby you usually get your books and you work out all your locks and stick plastic protectors over powerpoints - but we've all been around these heaters and most likely been poisoned at one stage and just never realised it."
In the years since her sons passed away, Vanessa has pushed for legislative changes and raised awareness of carbon monoxide poisoning through the charity she set up in her sons' honour: The Chase and Tyler Foundation.
And while the laws the Melburnian campaigned for - mandatory biannual servicing of gas heaters in rental properties - have not been legislated, she has been steadily getting the gas safety message out to more about more people. However, she still has more people to reach.
A recent study of Australian homes commissioned by Nest found that of all states and territories, those in Victoria were most at risk of CO poisoning, with almost half of homeowners surveyed revealing they don't know what carbon monoxide is.
Her number one piece of advice? Get your gas heater and gas-fuelled appliances serviced every one to two years. And if you live in a rented home, insist that the landlord and real estate agent arrange for this to be done.
"Before you move into a rental property, they should be servicing that appliance or they should be providing information on when it was last serviced so I'd be asking the real estate or landlord when it was last serviced," Vanessa told Mamamia.
"And if it hasn't happened in the past two years I'd get onto that straight away. Put it in writing, so you've got evidence of your request. Whether you're a tenant or a landlord it's just common sense to do this.
"Add it to your routine and that way you know your family is going to be safe."
Apart from getting your appliances serviced regularly, Vanessa, who has worked with Energy Safe Victoria to boost awareness, said you should make sure your home is properly ventilated and no vents have been covered or painted over.
She also suggests purchasing a CO detector, which range in price from $40 at Bunnings to top of the line ones from Nest for $180. They're designed to help warn people that the flu-like symptoms they're experiencing - dizziness, nausea, headaches, shortness of breath and confusion - are actually the early signs of carbon monoxide poisoning.
You can learn more about carbon monoxide poisoning prevention, including the signs of unsafe appliances and the symptoms of CO poisoning at The Chase And Tyler Foundation.