Background: Hygiene Requirements in Air-Conditioning and Ventilation Technology

On 01 January, 2018, a new edition of the VDI ("Verein Deutscher Ingenieure" = Association of German Engineers) guideline 6022 Part 1 on the hygiene of ventilation systems and air conditioners was published. The document underwent substantial revisions and now contains many new obligations for manufacturers, planners, constructors, operators and supervisors of HVAC systems and air conditioners.

The workplace ordinance ArbStättV ("Arbeitsstättenverordnung") regulates the erection and operation of workplaces for the safety and protection of employee health. For ventilation systems, this includes the maintenance (service, inspection, repair or improvement) of the workplace in order to maintain its structural and technical state.

This means that room ventilation systems (HVAC systems) must be tested for their functionality on a regular basis. They must supply healthy air and operate reliably. The aforementioned VDI guidelines are used for this. They describe how HVAC systems are to be operated and maintained. Therefore, VDI guideline 6022 serves employee protection and not so much product protection from a GMP point of view.  

Since the hygiene guideline VDI 6022 came into force in 1998, countless old facilities have been upgraded. These days, new facilities usually comply with the state of the art described in the guideline. However, since the state of the art keeps developing, the guideline has been revised and updated several times, already. In 2006, the first elaborate revision was made and in 2011, the guideline was revised editorially. Part 1 of the guideline has gained nine supplements. Every five years, the VDI guidelines are being subjected to an internal review in order to check if they still reflect the state of the art. During this, the main part (Part 1) as well as Part 6 (decentralised humidifying) were revised by the competent VDI working group and published as drafts in early 2017. Due to the public inquiry procedures, the drafts were modified once more. The final version of the main part (Part 1) was published in January 2018.

Compared with the old version of 2006/2011, there have been countless changes. Many of these changes aim to clarify unspecific wording or offer comprehensive descriptions of issues which had formerly only been mentioned in passing. Moreover, there is a great number of significant changes which will make the operation of HVAC systems safer from a hygienic standpoint in the future.

After the publication of the last version in 2011, there have been several important additions to Part 1, which were laid down in supplements: Supplement 1.1 describes the testing of HVAC systems, Supplement 1.2 offers notes on underground pipes and components and Supplement 1.3 focuses on the cleanness of air-touched surfaces. These Supplements are now included in Part 1, thereby eliminating duplications and streamlining the text overall.

Recooling systems, even if connected to a HVAC system, are no longer in the scope of VDI 6022. These systems have had their own guideline for two years: VDI 2047 Part 2. Domestic ventilation units are now definitely in the scope of VDI 6022. There is an explicit reference to DIN 1946 Part 6. Domestic ventilation units which are marked with the category "H" as per DIN 1946-6 are also compliant with the requirements of VDI 6022 Part 1 (Section 9.1).

Below are some examples for the numerous clarifying changes:

• Section 7.2: A comprehensive checklist was developed for initial hygiene inspections (Tab. 7)
• Section 7.2.1: The established design tests of components for conformity with the hygiene requirements of this guideline are commended as support for manufacturers of components. The overall state of the facilities must further be determined during the initial hygiene inspection.
• Section 7.3: The essential contents for the documentation of hygiene controls are listed.
• Section 7.6.6: The permanent dosing of disinfectants in air humidifiers is not permitted.
• Section 8.3: The surface sampling of germs is described more clearly and supplemented by recommendations for measures.

Two examples for innovations:

• Section 5.4: So far, it was only required that the supply air quality IDA may not be below the quality of the outdoor air resp. reference air. When the outdoor air quality ODA (cf. scientific paper "WHO Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide") is bad, the outdoor air drawn in must be improved. This may be accomplished by using a gas filter (active carbon filter), for example (Section 6.3.9.1).
• Section 7.1: The formerly strict intervals for hygiene controls of the individual facility elements have now been softened: depending on the risk assessment result, intervals may be reduced or increased. The latter, however, requires a sound air-hygiene opinion by a trained and competent person.

Particularly important innovations include:

• Generally, the workplace regulation has always required a risk assessment for ventilation systems. However, it can hardly ever be found in practice. They are supposed to be performed by an expert (at least training as per VDI 6022 cat. A), based on the (initial) hygiene inspection and the documentation/operating instruction of the manufacturer/constructor. The risk assessment primarily relates to maintenance staff, e.g. during the cleaning with chemical substances or when coming in contact with microorganisms (e.g. during filter changes or the cleaning of the humidifying chamber). The employer has to establish protective measures corresponding with the risk assessment results. He has to specify personal protective equipment for each individual case, write operational instructions and instruct his employees therein. This issue is discussed in detail in its own Supplement B on 4 pages. Persons who breathe the supply air are also subject to the risk assessment.
• In order to be able to evaluate changes in the air quality due to an HVAC system, appropriate measurements of the supply air at exemplary supply air inlet openings are necessary (Section 8.4). The requirements for the measurement staff as well as the sampling and the evaluation are described. It's noteworthy that a differentiation at least of the species of mould is mandatory. This presents much higher requirements for the analysing laboratory than before; furthermore, the cultivation in selective mediums may only take place in laboratories which are approved as per §44 Law on the Prevention of Infection.

Hygiene trainings must now also take account of the guideline changes. The VDI is therefore revising Part 4 (Trainings) at the moment. All persons dealing with HVAC systems such as planners, plant manufacturers, operators or supervisors are urged to catch up on the changes of VDI 6022.