Why limits are so important
The RLU value (Relative Light Units) is a quantitative measurement of the amount of ATP on a surface. Without defined limits, an RLU value is meaningless — you don't know whether 150 RLU is good or bad. Limits turn ATP monitoring into an objective decision-making tool.
Two zones: PASS and FAIL
Surface is clean. Production can start.
Surface is not sufficiently clean. Re-clean and retest. Do not start production.
Recommended initial limits from Charm Sciences TECH-137
| Surface type | Pass/Fail limit (RLU) |
|---|---|
| Stainless steel | 1000 |
| Teflon/PTFE | 4500 |
| Plastic | 2500 |
| Aluminium | 6000 |
| Rubber/silicone | 4500 |
PASS = RLU ≤ limit · FAIL = RLU > limit. These starting values are based on Charm Sciences TECH-137 and must be validated with accompanying microbiological testing (SPC/APC/RODAC).
Adjusting limits — when and how
After baseline study
Conduct a minimum of 6 measurement cycles and calculate mean + 2× standard deviation. This value is your validated Pass/Fail limit.
At product changeover
Different products leave different amounts of ATP. Validate limits separately for each product.
When changing cleaning agents
New chemicals can affect ATP measurement. Conduct a new baseline study after any change.