Many manufacturing processes require very strict environmental conditions provided by clean rooms. Because clean rooms have complex mechanical systems and high construction, operation and energy costs, it is important to systematically design clean rooms:
First step: Assess the personnel/material flow layout
It is important to assess the flow of people and materials in the clean room. Clean room staff is the source of pollution in clean room. All key processes should be isolated from personnel exit and passageway.
The most critical Spaces should have a single access to prevent the space from becoming a gateway to other non-critical Spaces. Some pharmaceutical and biopharmaceutical processes are susceptible to cross-contamination by other pharmaceutical and biopharmaceutical processes. Process cross-contamination requires careful evaluation of raw material inflow routes and containers, material process isolation, and finished product outflow routes and containers.
Step 2: Determine space cleanliness classification
In order to be able to select a clean room classification, it is important to know the main clean room classification criteria and what the particle performance requirements are for each clean room classification. Institute of Environmental Science and Technology Standard 14644-1 provides different cleanliness grades (1, 10, 100, 1000, 10000, 100000) and allowable amounts of different particle sizes.
Space cleaning classification has a great impact on the construction, maintenance and energy costs of clean rooms. It is important to carefully assess rejection/contamination rates under different cleanliness grades and regulatory requirements, such as the US Food and Drug Administration (FDA). In general, the more sensitive the process, the more stringent cleaning classification should be used. This table provides a breakdown of the cleanliness of various manufacturing processes.
Your manufacturing process may require a more stringent cleanliness grade depending on its unique requirements. Be careful when assigning cleanliness levels to each space; The classification of cleanliness between connecting Spaces should not exceed two orders of magnitude. For example, 100,000 clean rooms to 100 clean rooms is not acceptable, but 100,000 clean rooms to 1,000 clean rooms is acceptable.
Step 3: Determine space pressurization
Maintaining a positive air space pressure, with adjacent dirtier clean sorting Spaces, is essential to prevent contaminants from seeping into the clean room. When a space has neutral or negative space pressurization, it is difficult to keep the space clean sorting consistently. What's the pressure difference between the Spaces? Various studies have assessed the relationship between pollutant infiltration into clean rooms and the spatial pressure difference between clean rooms and adjacent uncontrolled environments. These studies found that w.g. pressure differentials of 0.03-0.05 were effective in reducing the infiltration of contaminants. The space pressure difference is above 0.05. w.g. does not provide significantly better control of pollutant infiltration compared to 0.05 in.
Keep in mind that higher spatial pressure differentials have higher energy costs and are harder to control. In addition, a higher differential pressure requires greater force in opening and closing the door. A 3-foot by 7-foot door requires 11 pounds of force to open and close. Clean rooms may need to be reconfigured to keep the static pressure difference between doors within acceptable limits.
Step 4: Determine the space supply airflow
Space cleanliness classification is the main variable to determine the air supply flow rate of clean room. The air exchange rate of the clean room should take into account the expected activities of the clean room. Class 8 100000(ISO) clean rooms with low occupancy, low particle generation process, pressurization and active Spaces with adjacent dirty clean Spaces can be used for 15 class hours, while the same clean room with high occupancy, frequent in/flow, high particle generation process, or neutral space pressurization will likely require 30 class hours. The designer needs to evaluate his specific application and determine the amount of ventilation to be used. Other variables that affect the supply airflow to the space are the process exhaust flow, the infiltration of air through the door/opening, and the seepage of air through the door/opening. The Environmental Science and Information Technology Services Department has published the proposed ventilation rate in standard Edition 14644-4.
Step 5: Determine the space air discharge flow
Most clean rooms are under positive pressure, resulting in ventilation into adjacent Spaces with lower static pressure, and unplanned ventilation through power outlets, lamps, window frames, door frames, wall/floor interfaces, wall/ceiling interfaces, and access doors. It is important to know that the room is not sealed and that there are leaks. A well-sealed clean room will have a volume leakage rate of 1% to 2%. Is this a bad leak? Not necessarily. First of all, zero leakage is impossible. Secondly, if active air supply, air supply and exhaust risk control devices are used, there needs to be at least 10% difference between air supply and air supply to achieve static decoupling between air supply, air supply and exhaust valves. The amount of air lost through the door depends on the size of the door, the differential pressure on the door, and the tightness of the door (washer, door drop, closing).
Step 6: Determine space air balance
Space air balance is all air added to the space (supply, infiltration) and all air leaving the space (exhaust, filtration, reflux) equal.
Step 7: Evaluate the remaining variables
Other variables that need to be evaluated include:
Temperature: Clean room workers wear overalls or full rabbit suits over their regular clothing to reduce particulate matter production and potential pollution. Because they have extra clothing, it is important for workers to keep the space temperature low. The space temperature range of 66°F to 70° will provide a comfortable environment.