Your cleanroom passed its last classification audit. The particle counts at the required sampling locations were within specification. The certificate is current. And yet contamination events still occur — at final inspection, at the customer, or buried in a warranty claim that traces back to something that happened in the assembly room but cannot be pinpointed to a specific cause. This is the gap that ISO classification alone cannot close. It measures the air. It does not measure what reaches the product.

The metric that connects the two is particle deposition rate: the number of particles ≥ D μm that fall onto a surface area of one square metre in one hour. This is the direct link between the condition of the air in your cleanroom and the likelihood that a critical particle lands on your product during the time it is exposed. Everything else — the ISO class, the HEPA filtration efficiency, the air change rate — matters only insofar as it determines this number. Particle deposition rate is the variable your product actually experiences.

Why the empty cleanroom and the working cleanroom are different environments

In a cleanroom with filtered air supply and no people present, particle deposition is negligible. Particles smaller than 5 μm are carried out of the room with the ventilation airflow before they have time to settle. The room looks clean, measures clean, and is clean. Add people, and everything changes. Personnel are the dominant particle source in any occupied cleanroom — emitting skin-cell fragments, fibres from garments, and debris from tools and equipment with every movement. For macro-particles larger than 40 μm, ventilation cannot effectively remove them: they are too large and too heavy to be carried out before they settle. Operations — not the room design — determine the deposition rate for the particles most likely to cause functional product failures.

The Whyte-Agricola research, formalised in ISO 14644-17:2021, quantified this relationship. Two cleanrooms with identical “At Rest” ISO 14644-1 classification can have operational particle deposition rates differing by a factor of ten or more, depending on personnel activity, process dynamics, and equipment vibration. The classification tells you about the room when it is empty. The deposition rate tells you about the room when your product is at risk.

The contamination of a product surface depends on three variables: the vulnerable surface area, the particle deposition rate at that location, and the time of exposure during operations. These three variables determine whether a critical particle reaches your product. They are the inputs to the ISO 14644-17 calculation methodology. And they are all measurable — which means the contamination risk is calculable, not just qualitative.

From deposition rate to a decision

The first step is knowing what deposition rate your product can tolerate. This starts from the product: what is the critical particle size, the vulnerable surface area, and the maximum acceptable number of depositing particles during the exposure period? From these inputs, the maximum allowable deposition rate can be calculated directly — and from that, the required local air cleanliness expressed as an ISO class. Brookhuis’s Cleanroom Insight calculator at risk-engine.brookhuis.com performs this calculation in accordance with ISO 14644-17.

The second step is measuring the actual deposition rate in your cleanroom during operations — not at rest, not at an annual certification visit, but continuously, at the product surface, throughout every shift. APMON measures particle deposition rate in real time: particles ≥ 15 μm counted on a 50 cm² collection surface every four minutes, reported as a deposition rate and compared against the alarm limit derived from your product. When the limit is approached or exceeded, you know immediately — before the product moves on to the next process step.

What particle deposition monitoring is used for

Setting contamination risk-based alarm limits — derived from product sensitivity and exposure conditions rather than from convention or historical averages.

Real-time detection of deposition events — spikes caused by personnel activity, process disturbances, or equipment emissions, captured at the moment they occur with timestamp and magnitude.

Root cause investigation — a timestamped deposition event log that correlates spikes with shift activities, personnel entries, process steps, and maintenance events.

Cleanroom qualification and process validation — demonstrating that the operational deposition rate stays within the limit derived from product requirements, as required by ISO 14644-17.

Continuous process improvement — tracking deposition rate trends across shifts, personnel, cleaning cycles, and process changes to identify and eliminate contamination sources.

Particle deposition rate is not a monitoring metric. It is the metric that determines whether your product is contaminated. Everything else in cleanroom management exists to keep it within the limit your product requires.

Go to products

Your cleanroom passed its last classification audit. The particle counts at the required sampling locations were within specification. The certificate is current. And yet contamination events still occur — at final inspection, at the customer, or buried in a warranty claim that traces back to something that happened in the assembly room but cannot be pinpointed to a specific cause. This is the gap that ISO classification alone cannot close. It measures the air. It does not measure what reaches the product.

The metric that connects the two is particle deposition rate: the number of particles ≥ D μm that fall onto a surface area of one square metre in one hour. This is the direct link between the condition of the air in your cleanroom and the likelihood that a critical particle lands on your product during the time it is exposed. Everything else — the ISO class, the HEPA filtration efficiency, the air change rate — matters only insofar as it determines this number. Particle deposition rate is the variable your product actually experiences.

Why the empty cleanroom and the working cleanroom are different environments

In a cleanroom with filtered air supply and no people present, particle deposition is negligible. Particles smaller than 5 μm are carried out of the room with the ventilation airflow before they have time to settle. The room looks clean, measures clean, and is clean. Add people, and everything changes. Personnel are the dominant particle source in any occupied cleanroom — emitting skin-cell fragments, fibres from garments, and debris from tools and equipment with every movement. For macro-particles larger than 40 μm, ventilation cannot effectively remove them: they are too large and too heavy to be carried out before they settle. Operations — not the room design — determine the deposition rate for the particles most likely to cause functional product failures.

The Whyte-Agricola research, formalised in ISO 14644-17:2021, quantified this relationship. Two cleanrooms with identical “At Rest” ISO 14644-1 classification can have operational particle deposition rates differing by a factor of ten or more, depending on personnel activity, process dynamics, and equipment vibration. The classification tells you about the room when it is empty. The deposition rate tells you about the room when your product is at risk.

The contamination of a product surface depends on three variables: the vulnerable surface area, the particle deposition rate at that location, and the time of exposure during operations. These three variables determine whether a critical particle reaches your product. They are the inputs to the ISO 14644-17 calculation methodology. And they are all measurable — which means the contamination risk is calculable, not just qualitative.

From deposition rate to a decision

The first step is knowing what deposition rate your product can tolerate. This starts from the product: what is the critical particle size, the vulnerable surface area, and the maximum acceptable number of depositing particles during the exposure period? From these inputs, the maximum allowable deposition rate can be calculated directly — and from that, the required local air cleanliness expressed as an ISO class. Brookhuis’s Cleanroom Insight calculator at risk-engine.brookhuis.com performs this calculation in accordance with ISO 14644-17.

The second step is measuring the actual deposition rate in your cleanroom during operations — not at rest, not at an annual certification visit, but continuously, at the product surface, throughout every shift. APMON measures particle deposition rate in real time: particles ≥ 15 μm counted on a 50 cm² collection surface every four minutes, reported as a deposition rate and compared against the alarm limit derived from your product. When the limit is approached or exceeded, you know immediately — before the product moves on to the next process step.

What particle deposition monitoring is used for

Setting contamination risk-based alarm limits — derived from product sensitivity and exposure conditions rather than from convention or historical averages.

Real-time detection of deposition events — spikes caused by personnel activity, process disturbances, or equipment emissions, captured at the moment they occur with timestamp and magnitude.

Root cause investigation — a timestamped deposition event log that correlates spikes with shift activities, personnel entries, process steps, and maintenance events.

Cleanroom qualification and process validation — demonstrating that the operational deposition rate stays within the limit derived from product requirements, as required by ISO 14644-17.

Continuous process improvement — tracking deposition rate trends across shifts, personnel, cleaning cycles, and process changes to identify and eliminate contamination sources.

Particle deposition rate is not a monitoring metric. It is the metric that determines whether your product is contaminated. Everything else in cleanroom management exists to keep it within the limit your product requires.

Go to products

Your cleanroom passed its last classification audit. The particle counts at the required sampling locations were within specification. The certificate is current. And yet contamination events still occur — at final inspection, at the customer, or buried in a warranty claim that traces back to something that happened in the assembly room but cannot be pinpointed to a specific cause. This is the gap that ISO classification alone cannot close. It measures the air. It does not measure what reaches the product.

The metric that connects the two is particle deposition rate: the number of particles ≥ D μm that fall onto a surface area of one square metre in one hour. This is the direct link between the condition of the air in your cleanroom and the likelihood that a critical particle lands on your product during the time it is exposed. Everything else — the ISO class, the HEPA filtration efficiency, the air change rate — matters only insofar as it determines this number. Particle deposition rate is the variable your product actually experiences.

Why the empty cleanroom and the working cleanroom are different environments

In a cleanroom with filtered air supply and no people present, particle deposition is negligible. Particles smaller than 5 μm are carried out of the room with the ventilation airflow before they have time to settle. The room looks clean, measures clean, and is clean. Add people, and everything changes. Personnel are the dominant particle source in any occupied cleanroom — emitting skin-cell fragments, fibres from garments, and debris from tools and equipment with every movement. For macro-particles larger than 40 μm, ventilation cannot effectively remove them: they are too large and too heavy to be carried out before they settle. Operations — not the room design — determine the deposition rate for the particles most likely to cause functional product failures.

The Whyte-Agricola research, formalised in ISO 14644-17:2021, quantified this relationship. Two cleanrooms with identical “At Rest” ISO 14644-1 classification can have operational particle deposition rates differing by a factor of ten or more, depending on personnel activity, process dynamics, and equipment vibration. The classification tells you about the room when it is empty. The deposition rate tells you about the room when your product is at risk.

The contamination of a product surface depends on three variables: the vulnerable surface area, the particle deposition rate at that location, and the time of exposure during operations. These three variables determine whether a critical particle reaches your product. They are the inputs to the ISO 14644-17 calculation methodology. And they are all measurable — which means the contamination risk is calculable, not just qualitative.

From deposition rate to a decision

The first step is knowing what deposition rate your product can tolerate. This starts from the product: what is the critical particle size, the vulnerable surface area, and the maximum acceptable number of depositing particles during the exposure period? From these inputs, the maximum allowable deposition rate can be calculated directly — and from that, the required local air cleanliness expressed as an ISO class. Brookhuis’s Cleanroom Insight calculator at risk-engine.brookhuis.com performs this calculation in accordance with ISO 14644-17.

The second step is measuring the actual deposition rate in your cleanroom during operations — not at rest, not at an annual certification visit, but continuously, at the product surface, throughout every shift. APMON measures particle deposition rate in real time: particles ≥ 15 μm counted on a 50 cm² collection surface every four minutes, reported as a deposition rate and compared against the alarm limit derived from your product. When the limit is approached or exceeded, you know immediately — before the product moves on to the next process step.

What particle deposition monitoring is used for

Setting contamination risk-based alarm limits — derived from product sensitivity and exposure conditions rather than from convention or historical averages.

Real-time detection of deposition events — spikes caused by personnel activity, process disturbances, or equipment emissions, captured at the moment they occur with timestamp and magnitude.

Root cause investigation — a timestamped deposition event log that correlates spikes with shift activities, personnel entries, process steps, and maintenance events.

Cleanroom qualification and process validation — demonstrating that the operational deposition rate stays within the limit derived from product requirements, as required by ISO 14644-17.

Continuous process improvement — tracking deposition rate trends across shifts, personnel, cleaning cycles, and process changes to identify and eliminate contamination sources.

Particle deposition rate is not a monitoring metric. It is the metric that determines whether your product is contaminated. Everything else in cleanroom management exists to keep it within the limit your product requires.