Prior to draining a refrigeration installation scheduled for dismantling and containing 6 tons of ammonia, a 5-kg NH3 leak occurred while employees were attempting to extract a sample at the level of the liquid separator, for purposes of performing a qualitative analysis. The leak occurred when a protective shell was removed. This pressurized shell had been installed to enable connecting a relief valve to a test flange. Firefighters closed the valve with a pipe clamp. Twelve people were evacuated from adjacent offices and no casualties reported. A specialized company was contracted to extract the samples and then drain the installation.