Introduction
For commercial ventilation hygiene contractors in the UK, understanding regulatory standards is vital for maintaining high service quality and compliance. For many years, the industry operated under a single general guideline: BESA TR19. However, as building science, fire safety awareness, and indoor air quality (IAQ) demands evolved, BESA divided the framework into two distinct, highly specialized standards: TR19® Grease and TR19® Air.
While both standards share the overarching objective of maintaining clean, safe ventilation infrastructure, their technical requirements, testing methodologies, measurement units, and reporting procedures are fundamentally different.
For field engineers and office managers, managing these dual requirements within a single operational workflow can be challenging. Using the wrong testing method or mixing up reporting criteria can result in non-compliant documentation.
This guide breaks down the core distinctions between TR19 Grease and TR19 Air and explains how modern field reporting software simplifies dual-standard compliance.
Core distinction: fire risk vs. indoor air quality
To understand the measurement differences, one must first understand the primary hazard each standard addresses:
| Feature | TR19® Grease | TR19® Air |
|---|---|---|
| Primary focus | Fire prevention and fuel-source removal | Indoor air quality (IAQ) and health hygiene |
| Target systems | Kitchen extract systems (canopies, ductwork, fans) | Supply, extract, and recirculation air systems |
| Main hazard | Flammable grease and carbon accumulation | Dust, particulate matter, mould, bio-aerosols |
| Testing tool | Wet film thickness gauge (WFTG) | Vacuum test (PVT) / deposit thickness gauge |
| Key metric | Micrometres / microns (µm) | Mass density (mg/m²) or micron thickness |
Deep dive: TR19® Grease standards and metrics
Kitchen extraction systems pose a severe fire hazard because cooking vapours condense into highly combustible grease layers along the inside of exhaust ductwork.
Key measurement criteria
Measurement tool. A calibrated wet film thickness gauge (WFTG), a comb-like tool pressed into wet or semi-solid grease deposits to measure depth.
Action thresholds.
- Measurement limit: any single reading exceeding 200 microns (µm) indicates that complete cleaning is required.
- System action level: if the mean deposit thickness across the system reaches or exceeds 200 microns, urgent cleaning must be scheduled.
- Post-clean target: following a professional clean, the surface deposit level must be reduced to less than 50 microns.
Frequency. Inspection frequency is determined by daily operational hours, ranging from quarterly for heavy 12–16 hour daily kitchen use, to annually for light 2–6 hour use.
Deep dive: TR19® Air standards and metrics
TR19 Air covers general ventilation systems supplying fresh air to, or extracting ambient air from, commercial offices, hospitals, schools, and residential towers. Here, the focus is preventing sick building syndrome (SBS) and limiting airborne contaminants.
Key measurement criteria
Measurement methodology. Inspection relies on dust accumulation measurements, often using the preferred vacuum test (PVT) or specialised gravimetric dust mass analysis, alongside deposit thickness gauges designed for dry particulate matter.
Action thresholds.
- Supply air systems: lower tolerance thresholds apply because incoming air directly affects occupant health. Dust mass accumulation exceeding 6 mg/m², or deposit thickness above 60 microns, generally triggers a cleaning requirement.
- Extract air systems: slightly higher tolerances apply, with action limits typically set around 15 mg/m² or 80 microns.
- Post-clean target: surface dust levels must be restored to strict baseline cleanliness standards, typically under 1 mg/m² or negligible micron readings.
Air quality auditing. This may involve biological surface sampling (swab testing for bacteria and fungal spores) in high-purity environments such as hospital operating theatres or pharmaceutical laboratories.
Operational challenges of dual compliance
For field service teams offering comprehensive HVAC maintenance, switching between TR19 Grease and TR19 Air protocols on the same commercial site presents clear operational risks:
- Confusing test units. Engineers entering dry particulate mass (mg/m²) into a field form designed for grease film thickness (µm) corrupts the record.
- Different photographic rules. TR19 Air requires detailed evidence of supply diffusers, air handling units (AHUs), filter banks, and attenuation silencers. TR19 Grease focuses heavily on canopy discharge points, plenum chambers, horizontal runs, and extract fans.
- Mismatched certificate templates. Issuing a TR19 Grease certificate for a general office supply system clean is a regulatory error that will fail an external audit.
How CertaVent streamlines dual-standard compliance
Rather than forcing field engineers to remember distinct paper forms or adapt generic PDF editors, CertaVent provides digital workflows tailored to each standard:
- Separate inspection paths. When a job is TR19 Grease or TR19 Air, the field screens follow that standard’s components, readings, and evidence.
- Standard-specific limits. Grease work is judged in microns. Air work uses the cleanliness class, flow type, and the test method chosen for that system.
- Guided evidence. The visit asks for the parts that belong to that job, such as canopy, duct, and fan evidence on a kitchen extract, or air handling units and test points on a ventilation system.
- The matching report. The office issues the certificate and post-clean report for the standard on the job, so a kitchen extract and an office supply system are not written up on the same form.