Originally dispatched as a Full Still for a chlorine leak. Villa Park responded with Engine's 963 and 962. Oakbrook Terrace ambulance called to scene for 2 patients exposed. Hazmat Box requested by 963-A. I responded as a tech and took the entry sector and Mike, who was on the OBTR ambo and became part of entry team 1 that mitigated the incident. One ton cylinder was being connected by public works at the water treatment plant when it started leaking. All in all, ended up being a faulty hose connected to the cylinder.