(28)To implement the Protocol, including the gradual reduction of the quantities of HFCs, the Commission should continue to allocate quota to individual producers and importers for the placing on the market of HFCs, ensuring that the overall quantitative limit permitted under the Protocol is not exceeded. The Commission should be able, exceptionally, to exempt for up to 4 years from the quota requirements of HFCs for use in specific applications or specific categories of products or equipment. It should be possible to renew that exemption if, after assessment of a new substantiated exemption request, the Commission, through the committee procedure, concludes that alternatives are still not available. To protect the integrity of the gradual reduction of the quantities of HFCs placed on the market, HFCs contained in equipment should continue to be accounted for under the quota system.