creating the perfect environment - technical notes #24 - 2

CONTROL OF LEGIONELLA WITHIN VINDON ENVIRONMENTAL CABINETS and ROOMS

12/10/04

 

1.0 Introduction

Vindon Scientific use a combination of pure water systems and ultrasonic humidity generators to provide a humidified atmosphere within our environmental cabinets and rooms

The pure water system is designed to be of sufficient quality to prevent premature faults and damage to our ultrasonic humidification system and to remove nutrients for potential algal growth within the humidity generation system and working chamber.

The main type of Production of Pure Water utilised on Vindon Equipment is Reverse Osmosis, followed by High purity De-Ionisation and finally UV irradiation of the treated water.

At the outset of Vindon Scientific Limited first using ultrasonic generation of humidity, the H.S.E was consulted and they recommended that the document HS (G) 70 be complied with, when designing, installing and maintaining the water system, although they considered the volume of the generators be used to be of insignificant size compared with systems which had given rise to known instances of contamination, i.e. large air conditioning plants and hot water systems.

1.2 Production of pure water

Purified water is expensive to produce and does not store well. The maximum use of the purified water must be made to minimise running costs, but is essential for correct operation of the humidity generation system.

The water must also be stored and distributed correctly to avoid algal or bacterial growth. The use of storage tanks either inside or outside the pure water unit can pose problems with regard to algal and bacteriological growth. If the water is allowed to stand with no chlorine present, the purification system must keep the purified water moving and away from sources of light in order to reduce the risk of any problems.

The system accomplishes this by re-circulating the pure water to prevent stagnation and irradiates it with U.V light to kill algae and resultant bacteria which feed off the algae.

The systems we fit to our rooms are purchased from well established pure water system manufacturers and fitted in accordance with their instructions and recommendations.

1.3 Ultrasonic generation of humidity

The generators 'nebulise' the water so that it forms a dense vapour at the temperature of the water, the vapour is drawn into the room or cabinet using the air circulation fan(s) of the chamber. No outside air is used to ventilate the room. The water used to generate humidity is fed directly from the pure water system in proprietary pipe work recommended by the makers of the pure water system.

The amount of water in the generator is kept to a minimum (approx 450ml) to reduce the possibility of gross contamination.

The generator tank is emptied automatically every six hours in order to remove any possible sources of contamination and nutrient which may have settled on the surface of the water from the air within the room.

1.4 Room environment considerations

The Rooms are natural incubators by the nature of the set environment within them and even with the introduction of sterile water vapour from steam generators any surface which has an air-water interface can provide a breeding ground for organic growth.

The traditional method of generating steam although initially sterile, can harbour infection as the injected steam temperature drops below 45ºC on entering and mixing with the ambient air of the chamber. A second consequence of the vapour dropping in temperature is that condensation forms at the exit of the steam 'wand' and drip trays have to be provided, which also can harbour contamination if not cleaned and sanitised regularly.

The control of the quality of air which can enter the room from the surrounding area during a door opening is difficult and to reduce the possibilities of bacteria or algae growing from this air or from personnel entering the room , the design of the humidity disperser and drainage system is such to minimise surfaces where standing water could form.

The cooling coils of the room produce condensate water and this water is not pure as it can pick up traces of the samples and other materials from the environment. It is drained away immediately via drain pan at the rear of the room and not re-used, the drain pan must also be cleaned and sanitised regularly.

1.5 Cabinet environment considerations

The Cabinets are also natural incubators by the nature of the set environment within them.

The control of the quality of air which can enter the cabinet from the surrounding area during a door opening is difficult and to reduce the possibilities of bacteria or algae growing from this air the design of the humidity disperser and interior is such to minimise surfaces where standing water could form.

The cooling coils of the cabinet produce condensate water and this water is not pure (it can pick up traces of the samples and other materials from the environment). It is drained away immediately and stored for re-use in a small reservoir at the base of the cabinet.

This reservoir is a possible source of contamination and to prevent this occurring regular dosing of the reservoir via the filler is recommended within a proprietary chlorine tablet such as 'Aquasan'.

The cabinet operating instructions include details of dosing the reservoir.

1.6 Sample considerations

The Cabinets and rooms primarily provide a temperature/humidity challenge to the samples stored within them and to continually have high concentrations of disinfectants (chlorine and organo-chlorines) may cause adverse reactions to the packaging and/or the samples.

1.7 Test conditions considerations

The Cabinets and rooms are primarily set to one temperature/humidity combination for long periods if not the entire life of the room/cabinet. Typical values are listed below

+5ºC & AMB.%RH

25ºC & 60%RH

30ºC & 60%RH

30ºC & 70%RH

40ºC & 75%RH

The individual combination has a large influence at which contamination can multiply.

The general rule is that the higher the temperature/humidity the faster contamination will grow and this should be reflected in the frequency of cleaning.

2.0 INSTALLATION

The following guidelines are adhered to on installations:

  1. Piping of “Pure Water” is done in black nylon tubes only
  2. No brass, copper, aluminium or mild steel fittings to be used (even stainless fittings may contain brass inserts.
  3. On recirculation systems dead legs are kept as short as possible and accessible for maintenance, inspection and cleaning.
  4. All Pure Water Systems are supplied with a “BIOSTAT” chemical compound which must be flushed through the system (led to drain and not any storage tank) for about 2 - 3 hours before using the system or fitting deioniser cartridges.
  5. Pipes close to or interconnecting the various units must be clipped to supporting walls etc.
  6. UV tube housings are to be mounted as per instructions and such that the fluorescent tube can be removed.
  7. The system will require periodic cleaning which entails disconnecting the pipe-work and re-routing it. The installation layout should take account of this.

3.0 MAINTENANCE

The cleaning of tap water to remove impurities also removes chlorine, which is introduced into tap water to prevent algae build up and kill bacteria in standing water.

The pure water produced is susceptible to algae growth and bacteria build up particularly if stagnant (dead leg in system)

The regular dosing of the water reservoir of the humidity system in cabinets is recommended.

The regular (every 12 months) cleaning of storage container and pipe work is essential to maintain a high level of cleanliness in the system.

The P.M.I (Preventative Maintenance Inspection) , which is recommended for both rooms and cabinets includes a cleaning/sanitation protocol.

4.0 SAMPLE/ OPERATOR GUIDELINES

The way the room is used can also greatly affect the level of contamination.

The following guidelines are recommended.

  • All samples should be packaged in sealed containers
  • Wet or liquid samples should be in sealed containers and visible to the operators, so that spillages can be identified and quickly cleaned up.
  • Operators should be in reasonable health and wear clean clothing which is provided for the purpose of entering the room.
  • Footwear should be clean.
  • Personnel who are allergic to high humidities should not enter the rooms.
  • Doors should not be left open for long periods
  • The rooms should be placed in areas which have a clean atmosphere (laboratories)
  • No open trays of liquid should be left in the room.

5.0 CONCLUSIONS

5.1. The rooms and cabinets can never kept completely free of all contamination as bacteria is present all around, in our environment, but to maintain systems at or below acceptable limits is to implement a regular cleaning and inspection regime and to perform testing of systems for contamination to determine effectiveness of treatment and determine future maintenance intervals.

5.2. The maintenance records of the attending engineers should include sections for the observance of physical contamination i.e. condition of the various elements of the rooms systems and the treatment given, rather than just tick boxes.

5.3. Feedback from customers with comments and observations is always helpful when improving the design, operation and maintenance of our equipment.

Ian Baker

Technical Manager