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Let’s Make Sure Surfaces Are Really Clean


When ATP monitoring systems were first introduced into the professional cleaning industry, most industry leaders breathed a sigh of relief. For the first time, cleaning professionals could measure how clean surfaces really were.

Before we could test for ATP – adenosine triphosphate, an indication of the presence of life – that was not possible. Instead, most cleaning professionals and facility managers measured cleaning by appearance: if it looks clean, it must be clean.

Knowing this was not a reliable measurement system, cleaning professionals turned to other tools.

For example, if the facility looked clean but there were still concerns, surfaces could be swabbed, the swab sample placed in a Petri dish, the dish taken to a laboratory, and we would know the results after two to four days.

The problem with this method is that if a surface is contaminated with health-risking microorganisms, anyone touching those surfaces of concern could potentially become ill. Waiting up to four days for results left too many people vulnerable.

ATP measuring and monitoring systems, which look like large television remote controls, put those fears to rest. Most ATP monitoring systems are referred to as “rapid” monitoring systems and can provide results in 15 seconds or less.

It cannot be denied that ATP monitoring systems have helped the professional cleaning and facility management industries considerably. And their aid has become even more valuable today as facilities worldwide struggle to reopen and prove to building users that their properties are clean and healthy.

Although these systems do have many benefits, there are some caveats and issues we must be aware of to take full advantage of ATP technology. Let’s start with a better understanding of what these systems are and what ATP monitors do and do not tell us.

ATP monitors measure the concentration of light units generated by organic material or living cells (and even some dead cells) on a surface.

Similar to using a Petri dish, a surface is swabbed, but rather than sending the sample to the lab, the swab is placed into the monitor. Within seconds, a digital evaluation appears.

A high number indicates a large volume of organic material or living cells are present. This tells cleaning professionals and building managers that this surface needs more thorough cleaning.

A low reading indicates the opposite – there are likely few, if any, health-risking microorganisms on the surface.

But here’s what ATP monitoring systems do not tell us.

Although a surface may have a high reading, indicating considerable ATP is present, it does not tell us what types of microbes are present. Is it the flu virus? COVID? Norovirus? Or is it food proteins that have transferred from someone’s fingers on to a surface? If it’s food, the ATP indicated would most likely be harmless.

Nevertheless, most cleaning professionals and building managers now interpret any higher than usual findings as a “red flag” and assume potentially harmful microorganisms are present, even if that may not be the case. This means ATP monitors remain invaluable, even if they can be fallible.

Let’s dig a little deeper into some more issues that can come up when using ATP monitoring systems. For this we turn to Michael Wilson, vice president of AFFLINK, a leading supply chain and technology organization made up of janitorial distributors throughout the country. According to Wilson, these are some of the questions often asked about ATP along with their answers:

Can we get a low ATP reading in one area of a surface and a high ATP reading right next to it?

Yes, this happens frequently, and this can be very problematic. The cause is soil distribution. The soil, possibly containing harmful microorganisms, has moved slightly on a surface, or was never exposed to a nearby surface. So, one surface has a high reading and the nearby surface, a low reading. The best way to address this is to conduct more tests in the same general location. If high readings persist, the entire surface must be viewed as contaminated and recleaned.

How large of an area should be swabbed?

There are no standards or “best practices” for taking samples. What is often recommended is to test an area of about four inches by four inches. Also, pay attention, and use a little common sense, as to how a surface is used. This can impact the ATP reading.

For instance, the upper part of a doorknob would likely have more ATP than the bottom area. But that may not always be the case. Test all areas of the doorknob for a proper reading.

Can different ATP systems or brands report different findings?

Once again, there are no standards, and different machines use different metrics. For example, a high reading on one brand may be a 5, indicating there is a large amount of ATP on the surface, whereas another brand may have readings up to 10. A problem many cleaning professionals and building managers have is getting accustomed to using one brand of monitor and then switching to another assuming the numbers indicate the same thing. This is usually not the case. It is imperative to review the manufacturers’ instructions to understand what the readings indicate for each machine used.

Can an ATP reading on a surface be high, indicating potentially harmful microorganisms are present, but tests in a laboratory of that same surface indicate it is clean and safe?

Yes, this happens. A laboratory is a clean-room or controlled environment. Even the air circulated is filtered to remove pollutants and contaminants. ATP systems, on the other hand, test surfaces in a real-world environment. Airborne contaminants, climate, moisture, even nearby foot traffic can all impact ATP readings. Nevertheless, view a high reading as a red flag. The surface should be recleaned and continually monitored.

Realizing ATP monitors are valuable but not infallible, what’s the best way to get the most out of them?

Training and practice. AFFLINK distributors work with their customers to teach them how to use these tools skillfully and properly. Then the cleaning worker or facility manager must follow through and use them regularly. Proper training and ongoing practice helps prove just how valuable these tools can be.

Robert Kravitz is a frequent writer for the professional cleaning and facility management industries. He can be reached at