Meat processing company Kepak has confirmed a leak of ammonia vapour at its plant at Watergrasshill in Co Cork.
The company said an investigation is under way into the cause of the leak.
Around 40 staff working in the plant at the time were evacuated.
Half a dozen staff were seen by a GP the following day and offered 36 hours' leave.
However, the company said there is no concern for their health and no further safety issues.
Around 350 people are employed at the Condonstown plant, which processes beef.
The company said the leak occurred on Sunday night in a cold storage area. It described it as "minor".
Kepak said safety procedures were put in place while the leak was dealt with and there were no injuries to staff at the time.
However, staff starting the day shift on Monday morning detected what was described as "a lingering trace aroma" of ammonia.
A number were seen by a GP and offered leave.
The company said the incident has been reported to the Health and Safety Authority and to the Environmental Protection Agency.
A spokesman for the HSA said it had been notified of an incident by the company and its inspectors have been in contact with Kepak.