Rats in the canteen, water pouring from the ceiling and up from drains, filthy toilets and blocked fire escapes.
Video and photographic evidence shown to ITV Wales show floors in the factory under several inches of water, while electric lights remain on.
The workers who made the allegations say they told managers and health and safety representatives of the company but their concerns were ignored.
The furniture manufacturer fell into administration on October 8th after what it called "an unprecedented fall in sales in the course of the last 10 weeks."
We've been working in terrible conditions for the last six months and we haven't said a thing about it, and this is how they treat us.
The former workers at the factory who spoke to ITV Wales say videos dating from the last week of September show the conditions they were working in.
We've had rain water dripping off lights onto our heads, we've got videos of it.
We complained to the managers, to the health and safety, to the owners.
Another former Triumph worker, David Meredith, told ITV Wales: "We were working in water above our ankles."
In a statement, Triumph Furniture said it had "employed a full-time health and safety manager to ensure compliance with relevant laws and swiftly deal with any incidents, including bringing in professional pest control services."
The company also said footage of flooded floors and leaking roofs was taken after October 1st when Merthyr Tydfil was affected by heavy rain.
The video footage of the flooding is not representative of the working environment at the Triumph factory.
However, three of the videos seen by ITV Wales were taken on the morning of the 24th September by former Triumph worker Christopher Bell.
He says production continued on that day in the factory, after "several of them swept the water into the drains".
Photographs shown to ITV Wales include pictures blocked fire escapes inside the factory.
A 2018 Triumph corporate video depicts the company's factory in Merthyr Tydfil.
Photographs given to ITV Wales show filthy conditions in the factory's toilet facilities in the weeks running up to its closure.
In a response, the company said: “We have shared all of the information we have available in relation to these queries.