An air quality assessment report commissioned by TasTAFE found blocked air filters and poor airflow allowed carbon monoxide to peak to dangerously high levels inside the automotive workshops at the Campbell Street campus.
The report comes after a teacher and two students were hospitalised with carbon monoxide poisoning in November, requiring "significant" treatment in a hyperbaric chamber.
The report, authored by private consulting firm Environmental Service and Design, was released by the Australian Education Union on Friday
The union said officials sat on the report for months knowing levels were dangerous in the months before the hospitalisations, while staff had been raising concerns about fumes in the building for more than a year.
Tasmania branch president David Genford said the November poisoning was the second poisoning-induced collapse of the staff member in the workshop with TasTAFE neglecting to report an earlier August incident to WorkSafe.
"TasTAFE have plainly neglected their duty of care under the law," Mr Genford said.
"This was the foreseeable and entirely preventable result of TasTAFE's choice not to take workers' or students' safety seriously.
"TasTAFE knew better and still chose not to fix the air quality, knowing full well this could endanger workers' and students' lives."
The report identifies the building's general ground floor workshop as having a "low air exchange at 3.23 volumes per hour".
"This means that when the vehicles are started there may not be sufficient air for the general air extraction and the exhaust extraction to operate efficiently and vehicle emissions will build up in the workshop," it says.
The union said the build-up of carbon monoxide within the workshop due to substandard air exchange was compounded by carbon monoxide being drawn back into the building because of poor ventilation.
TasTAFE's automotive courses are run out of the lower levels of the Campbell Street campus, where running engines emit carbon monoxide fumes that are vented outside the building.
But the union said the building's air intake was near that vent, with workers believing this was how toxic air was recirculated back into the building, compounding existing problems.
"Staff on other levels of the building have also reported to TasTAFE that they have smelt fumes, felt unwell and suffered headaches," the union said in a statement on Friday.
Tasmania Skills and Training Minister Felix Ellis said the matter was under a WorkSafe investigation.
"TasTAFE provided notification immediately after the incident was confirmed and have provided a copy of the independent report," he said in a statement to AAP.
But Mr Genford said with classes to return in 2025, the building was still not a safe place to work or learn and called on TasTAFE to fix the systemic problems with air supply.
