The increased awareness of the indoor environment together with the introduction of legislation has created a requirement for standards and guidelines to be set.
The various standards and recommendations currently available are as follows:

HVCA TR/19 Guide to Good Practice Internal Cleanliness of Ventilation Systems – Requires regular specialist cleaning of Extract Systems based on usage. Section 7.35 shows the minimum recommended interval between specialist cleans (see table)

Usage Hours/day Frequency
Heavy 12-16 3 monthly
Medium 6-12 6 monthly
Light 2-6 Annually
Readings Description Action
Micron readings between 0 - 50 Clean Report
Micron readings between 50 - 200 Acceptable Monitoring scheduled
Micron readings between 200 - 300 Dirty Program cleaning
Micron readings between 300 - 600 Heavy Urgent cleaning
Micron readings 600+ Extremely Heavy ASAP Closure of system

EVHA Guide to Cleaning and Risk Management of Grease Extract Systems (2006) - Section 9 requires specialist cleaning of kitchen extract systems based upon the measurement of grease and oil deposits utilizing a Wet Film Thickness Test gauge (see table)

AIB (Association of British Insurers) recommends that an extract system in a commercial kitchen should be cleaned and certified anything from annually to monthly, depending on the usage load.

Health Technical Memorandum HTM 03-01 – Specialised ventilation for healthcare premises Part B : Operational management and performance verification has introduced new practices for the management of healthcare ventilation systems. Critical care systems are now to be inspected on a quarterly basis and all systems are to be inspected on an annual basis. Findings should be recorded and areas with visible dirt or deposits should be cleaned.

Health and Safety Guidance Notes 202 General Ventilation in the Workplace, Guidance for Employers “as a general rule, if you run your finger along the opening of a duct and it collects dust then it probably needs cleaning”.

CIBSE TM26: 2000 Hygienic maintenance of office ventilation ductwork

EVHA Cleaning and Hygienic Management of Ventilation Systems

NADCA Assessment, Cleaning and Restoration of HVCA Systems (2006)

Further details of these publications are in our reference section.