Introduction: Responder’s action during mass environmental chemical incident involves collaboration of multiple agency. They clean the exposure site, control public safety and safe lives. The health of the responder is also as valuable as the public and always been neglected. Hence, this study is to highlights the method used and challenges during the incidents. Methods: A modified Occupational Health Surveillance Programme designed by Baker and Matte (Thirteen Steps in designing and implementing an Occupational Health Surveillance Programme) was imple-mented. These method full fill the criteria of impossible further reduce exposure to known hazards and uncertain health effect of the offending chemicals. Two core workplace namely the source of chemical contamination locale and victims’ evacuation centre were identified. The exposed responder is identified and categorised according to their expected exposure. Offending chemicals identified were known hazardous to health. An electronic survey form was developed and the surveillance were conducted during the event and post-exposures of one, third and sixth months. Laboratory tests were performed as a grab sample randomly and strategically to represent responder exposure. Results: During the event, 1338 responders were surveyed and twenty percent had symptoms of cough, headache, sore throat, nausea and skin irritation. After one-month post-exposure, three percent of responder noted to have continue symptoms. Laboratory tests were performed randomly due to the sheer numbers of responders in action. Only sixty-one samples were collected and sixteen percent had positive metabolites for urine cyanide. Re-sponders with abnormal laboratory result (FBC/LFT/RP/Urine) were interviewed and a repeat sample were performed. Conclusion: The health surveillance of the responder in mass environmental chemical incident is a great challenge when the exposure level is unsure and involve more than one chemicals. Likewise, reliability and validity adopting statistical test for health surveillance instruments is unattainable due to urgency. However, a proper method of occu-pational surveillance need to be devised and implemented to ensure the protection of worker’s health is guaranteed.