(L) Owner of Thiens Alterations in Woden Thu Khanh Pham embraces (R) Samantha Diplock this afternoon.

HELPING HAND: Thu Khanh Pham and Samantha Diplock are reunited at Mrs Pham's Woden alterations shop on Tuesday after Sunday's near tragedy, the cause of which is being investigated. Photo: Colleen Petch

Doctors say Thu Khanh Pham was just minutes from inhaling a deadly amount of poisonous gas when Samantha Diplock found her, collapsed near the counter of her Woden alterations shop.

The carbon monoxide was creeping into Mrs Pham's store, and into her lungs, from a faulty boiler in a neighbouring dry cleaners at Bonner House, adjacent to Woden Plaza, on Sunday.

Mrs Pham's memories are fuzzy, but she can recall feeling dizzy, and trying to walk outside to get fresh air, before blacking out.

The next thing she remembers is waking up in a hospital bed and, in a dazed state, quickly demanding she be allowed to return to her shop to lock the doors.

It was not until later on that Mrs Pham was told that one of her customers, then a near stranger, had saved her life with basic first aid skills.

''Without her, I think I might be dead already,'' Mrs Pham said.

''About five minutes more and it was going to be too late.''

Mrs Diplock, a public servant from Lyons, had gone to the alterations store on Sunday to drop off trousers.

She noticed Mrs Pham on the floor and another man, who would later also collapse, standing next to her.

''I said 'is she all right?', and he just wasn't saying anything at all,'' Mrs Diplock said.

''So I rolled her into the recovery position and all this vomit came out … I was glad I rolled her over, because I remember from doing a Royal Life Saving resuscitation course that I have to keep her airway clear,'' she said.

''If I hadn't rolled her on her side she might have choked and died.''

Mrs Diplock called triple-0 and stayed with Mrs Pham, checking whether she was conscious, and ensuring she didn't roll onto her back again.

The pair were reunited for the first time at the Thiens Alterations Store on Tuesday afternoon.

They embraced like old friends, before Mrs Pham said: ''I wouldn't be here if it wasn't for you.''

Needless to say, Mrs Diplock is receiving free alterations for the foreseeable future.

Mrs Pham was back at work on Tuesday, and was receiving many calls from customers asking about her health.

Work at the neighbouring dry cleaners has been shut down by WorkSafe ACT while the incident is investigated.

The initial inquiries have found the faulty boiler leaking the carbon monoxide had been inadequately maintained.

WorkSafe inspectors are now preparing to inspect maintenance records for all similar boilers used across the ACT.