How the negative pressure container ventilation system works?

The basic principle of the negative pressure system is to keep the pressure of the environment inside the container lower than that outside, so that the toxic gas or flammable gas in the container will not be directly discharged from the it, and the negative pressure system captures dangerous and infectious particles in the air, and it is removed with a blower and a set of filters.
The negative pressurized container provide by TLS typically has 2 fans, a small fan for normal mode and a large fan for emergency mode. When either fan is turned on, a negative pressure environment is formed inside. When only the small fan in the fume hood is turned on, the internal pressure is around -30~40Pa, and normal ventilation mode in the container; When the flammable gas/H2S low level alarm is triggered, the outdoor Ex-fan will automatically turn on, the internal pressure is around -130Pa and the container enter the emergency mood and it will automatically turn off when the gas concentration is lower than the set value. If the gas concentration does not decrease, the high-level alarm of flammable gas/H2S would sound, after the alarm lasts for 10 seconds, the power supply of the container will be cut off.
Negative pressure is a safe sealing solution which is widely used in lab containers, Mud Labs, etc.