During 2003, different plastic stemming plugs (Cats, Stemtite, and Taponex) were tested in Escondida's Mina Sur, to determine the effect on gas retention time when used in conjunction with drill cuttings in production shots with a blasthole diameter of 10 5/8. Longer retention times were expected to provide greater fragmentation and muckpile looseness. In order to determine which plug showed the greatest enhancement of stemming retention, 17 trials were carried out - in the first seven tests, only the Cats were used, in the following five tests, a combination of Cats, Taponex and Stemtite were used, and in the last three tests, only the Taponex plug was used. In the last two blasts, drill cuttings were used without stemming plugs as a benchmarking exercise._x000D_
Blasts were filmed with a high-speed camera, which could record the detonation times of holes using rolls of shock tube tied to stakes at the hole collars, to act as flash indicators. The camera allowed measurement of the time between charge detonation and the commencement of stemming ejection._x000D_
In order to obtain the statistical parameters of each one of the stemming plugs used in the 17 trials carried out, the Minitab software was used and a data base was created for it, corresponding to each stemming configuration with the retention time obtained from the filming._x000D_
Once it was determined which stemming plug provided the greatest enhancement of stemming retention, the impact on the fragmentation was analysed using the WipFrag image analysis software to estimate the muckpile size distribution.