The Department of Agriculture ordered the slaughter of 6,000 chickens at a farm at Knockatallon, Co Monaghan, last week in an exercise to test local readiness for a possible outbreak of avian flu.
Officers from Co Monaghan Fire Service headed the operation, wearing chemical-proof suits and special breathing apparatus to protect them from the lethal CO2 gas they were using to carry out the extermination of the flock.
"The chickens used for the exercise were past the end of their productive life," the department said, and were deemed suitable for the fact-finding operation.
It said the gassing proved to be an acceptable and humane way of disposal.
The region is on what is being called a "bio-alert" for any outbreak of avian flu. Some 60 per cent of all poultry produced nationally comes from Co Monaghan.
The department stressed that the flock involved had no infection of any type.
Both the department and fire service said the operation - to test not only their reaction but also the effectiveness of the gas - was a success.
Last week Sinn Féin TD for Cavan-Monaghan Caoimhghín Ó Caoláin announced that the many hundreds of poultry workers in the area would be able to avail of free inoculation against the bird flu.
He made the announcement after meetings with the department, where he expressed the worries of workers in the industry to the Minister.