The main precautions are:
(i) Every possible care should be taken to see that steam is perfectly dry before passing into water.
(ii) The calorimeter should be properly insulated by keeping it within a wooden box provided with a sliding lid with two holes and lined inside with a layer of cotton wool, cotton pad, etc.
(iii) Steam should no longer be passed when temperature of water in the calorimeter rises approximately by 20°C.
(iv) While passing steam, care must be taken that condensed steam does not escape out.