The "hidden flaw" in modular cleanroom installation—air leakage under the door.

The core operational prerequisite for modular cleanrooms is maintaining tight airtightness and a stable pressure gradient to ensure compliance in production and experiments. They are widely used in demanding cleanliness fields such as pharmaceutical, electronics, and biological laboratories. As the core barrier between clean and non-clean areas, the door's sealing performance directly determines the cleanroom's operational stability. Air leakage at the bottom of the door is the most common detail-related failure during installation. Based on industry standards and practical experience, this is explained in detail below.

Air leakage at the bottom of the door refers to the phenomenon where, after the modular cleanroom door is closed, a gap exists between the bottom of the door and the ground, causing air convection between the clean area and the outside or adjacent areas. This gap is an active gap, affected by factors such as door opening and closing and ground flatness, and is a major source of air leakage in cleanrooms, directly impacting airtightness. According to relevant industry standards, the leakage rate at the bottom of the door should be ≤1.5 m³/h·m², the gap velocity ≤0.3 m/s, and the reserved gap should be controlled within 3-5 mm. Any gaps exceeding these ranges require immediate rectification.

Air leakage at the bottom of the door is mainly related to design, material selection, and construction techniques. During the design phase, failure to verify on-site conditions, lack of adjustable sealing structures or dedicated sweeping strips, and unreasonable door opening dimensions can easily lead to inherent hidden dangers. In terms of material selection, using ordinary rubber sealing strips instead of cleanroom-specific EPDM or silicone sealing strips, along with sealing strip cutting deviations and inferior sweeping strips, results in insufficient sealing performance. During construction, ground flatness deviations exceeding 1‰, improper installation of sealing strips, misaligned door installation, and failure to promptly detect potential air leaks are the main contributing factors to air leakage.

Air leakage at the bottom of doors can lead to uncontrolled cleanliness and pressure differential, causing indoor particle concentrations to exceed standards and making it impossible to maintain a pressure gradient of ≥10 Pa between clean and non-clean areas, and ≥5 Pa between adjacent clean areas. Statistics show that this accounts for 70% of cleanroom pressure instability problems. It also increases energy consumption, requiring air conditioning units and FFUs to operate at high loads, increasing energy consumption by 20%-30% compared to design values, and making temperature and humidity control difficult. Furthermore, it is a key rejection item for GMP and ISO 14644 certifications; failure to rectify it will result in certification failure and may also lead to product contamination, safety accidents, and economic losses.

The rectification of air leakage at the bottom of the door must follow a systematic approach: First, check the gaps at the bottom of the door, the flatness of the floor, and the damage to the sealing strips. Replace them with cleanroom-specific EPDM sealing strips and equip the room with an adjustable automatic sinking sweeping strip. Secondarily level the floor at the bottom of the door to ensure a flatness deviation of ≤1‰. Adjust the height of the sweeping strip to ensure the gap at the bottom of the door is ≤3mm. Apply cleanroom-specific sealant to the joints, and seal the gaps between the door frame and the wall with polyurethane foam. After rectification, use a smoke generator and an anemometer to ensure the air velocity in the gaps is ≤0.3m/s. Conduct 24-hour differential pressure steady-state monitoring and particle concentration testing. Once the tests are passed, establish a construction inspection record.

Prevention of air leakage at the bottom of the door must be integrated throughout the entire installation process. Optimize the sealing design during the design phase, select materials according to cleanroom-specific standards, strengthen detail control during the construction phase, and conduct timely testing after installation. Post-installation maintenance requires regular inspection of the door bottom seals and sweeping strips, timely replacement of aging components, and ensuring the long-term stable and compliant operation of the cleanroom.