In modern high-end manufacturing and scientific research fields, air filtration systems are facing unprecedented dual challenges: how to achieve sub-micron level ultra-high cleanliness while ensuring absolute fire safety in extreme situations? The integration of the UL900 Class 1 standard and HEPA /ULPA technology provides the ultimate answer to this core question, marking the transition of air purification technology from a single performance dimension to a systematic and mature era that prioritizes both safety and efficiency.
I. What is the UL900 Class 1 Standard?
UL900 is the “Standard for Flammability Safety of Air Filter Units” established by Underwriters Laboratories (UL). It evaluates the combustion characteristics of filters when exposed to open flames and their potential impact on fire spread. Its core value lies in transforming filters from potential fire “fuel” and “propagation channels” into passive safety barriers. To obtain Class 1 certification, the filter must self-extinguish quickly after the fire source is removed and not produce any burning droplets.
Core Classification and Testing Requirements:
UL900 classifies filters into two levels based on their combustion performance, with Class 1 being the highest safety level:
| Characteristic | UL900 Class 1 (Flame Retardant) | UL900 Class 2 (Flammable) |
| Burning Time | Flame self-extinguishes within 10 seconds after fire source removal | Flame burns for a longer time |
| Burning Droplets | No burning droplets produced | May produce burning droplets |
| Charred Length | Charred area length is strictly limited (≤ very short distance) | Charred area is longer |
II. How HEPA/ULPA Achieves the UL900 Class 1 Standard
Achieving UL900 Class 1 certification for HEPA/ULPA filters is a systems engineering project encompassing materials science, structural design, and manufacturing processes.
1. Breakthroughs in Material Technology
2. Traditional HEPA/ULPA filter materials (such as glass fiber) are not inherently flammable, but the resins used to bind the fibers and structural components may pose a risk. The key to obtaining Class 1 certification lies in:
- Flame retardant treatment: The filter material undergoes special impregnation treatment to form a carbonized layer that isolates oxygen when exposed to flames;
- Component safety: All components, including separators (using flame-retardant PET instead of aluminum foil), sealants, and frame coatings, must meet flame-retardant requirements;
- Non-toxicity guarantee: No large amounts of toxic fumes should be released during combustion.
2. Innovation in Filter Structure Design
At the Trenntech R&D center in Frankfurt, engineers have developed a fire-resistant filtration system specifically designed for high-risk environments:
Overall flame-retardant structure: Fire-resistant design for all components, from the filter material to the frame;
Enhanced sealing technology: Using special fire-resistant sealing materials to ensure that the seal remains intact even in high-temperature environments;
Structural reinforcement: Optimized support structure to prevent the filter from collapsing and blocking the air duct during a fire.
3. How to achieve a balance between fire safety and filtration performance?
- Efficiency maintenance: Flame retardant treatment must not significantly affect the collection efficiency and grading efficiency curve of the fibers;
- Resistance control: The treated filter material must still maintain low airflow resistance;
- Lifespan guarantee: Chemical treatment should not accelerate filter aging or reduce mechanical strength.
The integration of UL900 Class 1 and HEPA/ULPA technologies marks a fundamental evolution in risk management paradigms: from passive “failure response” to proactive “safety design,” and from isolated “functional components” to integrated “system barriers.” Choosing a rigorously certified fire-resistant filtration system is not only a technical decision but also a reflection of professional philosophy—it captures microscopic pollutants with a precise mesh and withstands extreme crises with a robust structure, providing dual protection for cleanliness and safety whenever needed.