One of the occupational safety and health in chemical laboratories is maintaining air conditions so that they are not contaminated by toxic gases. To optimize it, an IoT-based CO, CO2, CH4, and NH3 gas measuring instrument is designed using a Raspberry Pi 3, MQ-135 sensor, MQ-7 sensor, MQ-4 sensor, DHT22 sensor, buzzer, and LCD. The measurement data will be displayed on the Node-RED UI. The result is that the instrument can detect levels of CO, CO2, CH4, and NH3 gases, can measure room temperature and humidity, and also provide a hazard warning. The measurement results are the average measurements on 25 ml of liquid ammonia with a concentration of 25%. 50%, 75%, and 100% obtained values of 0.22 ppm, 0.50 ppm, 1.04 ppm, and 3.95 ppm, while at 25 ml of methanol with concentrations of 25%, 50%, 75%, and 100% obtained an average of 0.21 ppm, 1.97 ppm, 2.45 ppm, and 4.49 ppm. Another measurement result is the average measurement of CO and CO2 gas levels are 7.06 ppm and 5.05 ppm. The temperature and humidity sensor have an average measurement of 29.0°C and 70.7%. There is no delay in sending data from the Raspberry Pi to the UI NodeRED.