A tunnel is a confined space which may require a controlled atmosphere to guarantee a safe and healthy environment for temporary transit. there are road traffic tunnels, railway tunnels, utility tunnels and tunnel construction. These different applications have different requirements concerning which gases to be monitored and which gas monitoring technology to be applied. Besides explosion protection from combustible gases there is the potential hazard of accumulation toxic gases. We usually suggest the customer to detect flammable gas,H2S,CO and O2 in these environments