A cleanroom is a controlled environment specially designed to keep the concentration of contaminants to a minimum. So we are all on the same page, contamination can be defined as a process or an action that causes surfaces, instruments, or equipment to become soiled with contaminating substances.

These substances can include pathogens (germs, bacteria, toxins), threads and fibers, fluids, and soils, among other things. When on a surface, they can cause what is termed a “killer defect,” which can skew testing procedures and results conducted in the cleanroom. 

One of the key ways cleanrooms are kept contamination-free is by proper air flow and filtering the air released in the room. For instance, while the air in a typical office building may have 500,000 to 1,000,000 particles — 0.5 microns or larger — per cubic foot of air, a Class 100 cleanroom will be designed to never allow more than 100 particles, 0.5 microns or larger, per cubic foot of air to be released in a cleanroom.

However, there is a lot more involved in keeping a cleanroom environment contamination free than just air flow and the number of microns in the air. Even when safeguards are taken, contamination in a cleanroom can still be generated by people, processes, equipment, the garments worn in a cleanroom, materials brought into the cleanroom, etc.

Further, very often the very tools and equipment used to keep the cleanroom clean are the culprits. This is especially true when floors are damp mopped. As the mopping procedure advances, the cleaning solution begins  to lose its efficacy. This means the cleaning solution becomes less effective as the floor is mopped.

But the big problem is the soiling of the mop and mop water as it is used over the floor. As the floor is mopped, and this starts as soon as the mop is used, the mop begins to collect and then spread soils as it becomes saturated.

The same thing can and does happen if cleaning cloths are used for a prolonged period to clean counters, instruments, etc. As they are used they become soiled and the same process — the spreading of contaminants — begins again.

We will discuss ways to prevent this from happening later in our discussion, but our big concern now is how do we determine if a surface is contaminated? Of course, we could swab a surface, place the swab in a Petri dish, and wait a few days for the results. But how many administrators can shut down a working cleanroom for that length of time?

Another option is to use what is referred to as an ATP rapid monitoring system. These systems have become very common in the professional cleaning industry. Often, they are used before cleaning begins and then again after cleaning has been performed. The results scientifically indicate the effectiveness of the cleaning procedure. Plus, help cleaning professionals know if more cleaning or a different form of cleaning is necessary.

Understanding ATP

Adenosine triphosphate (ATP) is an energy-bearing molecule found in all living cells. It was discovered by scientists in Germany and the U.S. nearly 100 years ago. If ATP is detected on a surface, it means living or dead cells are present, both of which can be viewed as contaminants. 

One of the drawbacks of ATP rapid monitoring systems is that they do not indicate precisely what types of contaminants are on a surface. They just suggest that contamination may be present. On the other hand, one of the key benefits of these systems is that they are so fast. Instead of waiting two to four days for test results, with some systems, results are available within 15 seconds or less.

The results will also indicate the levels of ATP on a surface. For instance, here is the scale used by one or more of the monitoring systems:

• If a surface has an ATP count of 35 or below after cleaning, it is considered “effectively cleaned.”
• A reading of 36 to 70 indicates “needs improvement.”
• If the reading is 71 or higher, the surface is considered “ineffectively cleaned.”

Using an ATP monitoring system

Most ATP monitoring systems look like a large TV remote control. In general, to use them the surface is swabbed and the swab is then placed in the system. However, there is a bit more to it than this. Among other things we should know are the following:

• Store swabs in a refrigerator at no more than 46 degrees Fahrenheit; if not refrigerated, swabs can be stored at room temperature for up to about four weeks.
• When conducting ATP testing, avoid leaving swabs at room temperature for more than 20 minutes.
• ATP systems may need to conduct a “self-test” for about 60 seconds when first turned on. Avoid using the unit until it has finished performing this test.
• For flat surfaces, swab a four-inch by four-inch area, moving the swab from left to right as well as up and down.
• For irregular surfaces such as door handles, swab enough of an area to collect a good sample.
• Rotate the swab as it is used so that all areas of the swab come into contact with the surface to be tested.
• After using the swab, place it in a tube, provided with most systems. Snap the top of the tube to release a liquid that protects the sample.
• Hold the tube vertically and shake it back and forth for about five seconds. 
• Keeping the swab upright, insert it into the monitoring device for testing.
• Wait approximately 15 seconds.

Working with the results

Let’s say we have taken an ATP reading of a cleanroom floor and the reading is 72. This reading is too high, indicating the floor has not been cleaned effectively, and therefore contamination is possible. Because the floor has just been cleaned in our scenario using a mop/mop bucket, we can assume the reason for the high ATP reading is the mopping procedure.

To eliminate mopping and attempt to reduce the ATP reading, we have two alternatives: use an automatic scrubber, or a less costly “autovac” floor cleaning system.

According to a report by the Clinical Laboratory and Nutritional Sciences Lab at the University of Massachusetts at Lowell, testing results using both systems found they “had significant (98 percent) reduction in the levels of ATP on the flooring tested.”

For the record, tests were also conducted using the traditional floor mopping method. According to the same testing lab, “the mop method had a minimal reduction in ATP (44 percent).”

If our high ATP reading is on a counter or similar flat surface, it may be caused by the cleaning cloth used to clean the surface, as mentioned earlier. Alternatives to using cleaning cloths to address this problem are cleaning tools such as chemical injection technologies that apply a cleaning solution to the surface. The flat surface area is then wiped clean using a microfiber squeegee.

Administrators and cleaning

Whereas managers of an office building or even a school may turn to a cleaning contractor to decide which cleaning methods and products should be used to clean the school, administrators of cleanrooms cannot do this. They must be very involved in the cleaning procedure to assure quality. As we know, improper cleaning can result in contamination, skewed research and testing results.

Work with your cleaning contractor to develop a scope of services, indicating what surfaces (areas) must be cleaned, how often, and using which cleaning solutions, products, and equipment. And don’t forget testing surfaces. In some cases, ATP testing may need to be performed throughout the week to ensure quality standards are maintained. But look at it as a cost effective insurance policy. ATP systems help ensure the work done in a cleanroom is accurate, saving time, money, and producing quality results.

Final notes

Different manufacturers of ATP monitoring systems may use different scales. Often a surface must be tested more than once to determine an accurate ATP reading. A cleanroom will have higher standards than, for instance, an office building. In such cases, an ATP reading over 35 may be fine in an office building, but indicate “ineffective cleaning” in a cleanroom.


Here are some of the ways humans spread contamination in cleanrooms:
• Fast motions, including horseplay
• Airborne skin flakes, oil, perspiration, hair
• Certain cosmetics and colognes
• Sneezing and coughing
• Work habits
• Electrical charges from people touching surfaces

Robert Kravitz has owned three contract cleaning companies in Northern California and has written two books on the professional cleaning industry. Today he is a frequent writer for the professional cleaning industry.