A bubble column is constructed and fitted with five sets of igniters and pressure sensors to study the ignition and explosion of hydrogen/oxygen bubbles in water. Two pressure-resistant glass windows are also fitted in the central section of the column for visualization of the ignition. A loop is built to circulate water through the column. A double concentric tube is used to feed oxygen, hydrogen, and water. Ignitions at different locations, oxygen/hydrogen molar ratios and flow rate are also performed. The results find that significant overpressure is generated when large oxygen/hydrogen bubbles or slugs contacted the fusing Nichrome wire igniter. The explosion overpressure also causes strong pulsation of the liquid in the whole column. Finely disperse bubbles are however prone to ignition and do not produce any overpressure. Co-current flow of water helps to minimize the formation of large bubbles or slugs and provides a safer means for reacting hydrogen and oxygen. The results are expected to be useful for scaling up the direct synthesis of hydrogen and oxygen into hydrogen peroxide. (c) 2008 Elsevier Ltd. All rights reserved.