IoT based Portable Manhole Gas Sensing System

Maintenance of sewage systems requires workers to enter confined manholes, where hazardous gases can build up. These toxic, flammable gases create a serious safety risk. To address this problem, a portable gas monitoring system based on IoT technology was designed for real time sensing and observation. The proposed system comprises of MQ- 4, MQ-6, and MQ-7 gas sensors, along with a DS18B20 temperature sensor, all interfaced to an ESP32 microcontroller. The data is then transmitted to a cloud platform built with Node.js and MongoDB, enabling real-time monitoring. Whenever the gas concentrations exceed the safety limits, alerts are triggered to enable early action. The experimental results show an accuracy of approximately ±2% compared to standard measurement instruments, with the latency less than 500 ms. Early warning of dangerous gas levels can significantly reduce risks during sewage maintenance.