Sources of chemical contamination and concentration levels
1. Outdoor air
Outdoor air contamination levels entering the incoming air to a cleanroom can include variable contamination levels from the same building exhaust, exhaust from neighbouring buildings, or other contamination sources including farms, sewer plants, dumps, highways, airports, train yards, local industry, and other sources. These levels can vary dramatically with wind direction, wind velocity, time of day, precipitation, temperature, sunlight or other factors. Thus it is important to use continuous monitoring where possible for the most important parameters, or to do periodic sampling on different dates and with sampling for many hours or days, so that atypical average or highest level can be assessed, rather than just a single data point.
ABN use long-term average data for predicting chemical filter lifetimes, and real-time data is valuable to assess the highest levels encountered to assess if they will affect the most sensitive products.