Wednesday 13 May 2015

Dusty builders in your technology room

We've been involved in many projects where a data centre room is built from scratch in a bare concrete building skeleton. There are many challenges involved in such projects, but the most insidious problem is dust created during the construction process. It gets everywhere; on floor slabs, ceiling voids, ducting, even installed cabinets. You need to have a clean room environment before the installation of servers and network equipment. It can contaminate fan bearings, printed circuit board surfaces If you install in an environment containing dust you risk premature equipment failure and malfunction.  It clogs filters in air conditioning units.

Once you get the room dust free through specialist cleaning of floors, voids, walls and ceilings it is difficult to keep it clean. Ideally you need to ban tradesmen/craftsmen from working in or entering the clean room once it has been fully cleansed. In practice however there will always be something delayed or forgotten which creates extra construction work in your precious "finished" room. If it is essential the contractors undertake any dust creating work you'll need to consider dust control tents, with dust extraction air handling, to enclose their work area. Their method statement documents should always detail how they'll control dust. Before releasing the work area you'll need to ensure appropriate cleansing to ensure the effected area is dust free. 

People carry dust on their clothes and shoes from the environment outside of the clean room. This is particularly the case if they've been involved in or working close to dust creating activities. You can use tack-mats inside the entrance doorway to trap dust from shoes. The mats need to be checked/renewed daily to ensure they're functioning properly. You also need to police the use of the tack-mats to make sure people are using them.

Disposable coveralls and booties for shoes will help to contain contamination dust, but tend to be unpopular with tradesmen if they need to frequently enter/leave the clean room. You'll also need facilities for people to change into and dispose of the cover clothing.  There are costs of these disposable items.

After some experimentation we devised a temporary two door air lock solution. The floor of the air-lock contains dust removal measures such as bristle mats mounted on a grounded metallic vacuum plenum matrix. The air lock chamber is temporarily assembled inside the main entrance to the clean room . As people enter the room, air knives blast air from their clothing and shoes. The bristles brush their shoes as they walk across and the underlying vacuum floor sucks away dust laden air through the bristle mat.

We treat the air by passing it through a dust vortex chamber and then on to a MERV 11 HEPA filter chamber to clean the air before returning it to the clean room. This arrangement does not alter the air pressurisation of the clean room. The vortex chamber extracts 99% of dust leaving the finer residue for the HEPA filter but it drastically reduces the maintenance needed to support the HEPA filter (extends life). The dust captured by the vortex chamber is dumped in a sealed container for easy removal by low skilled workers. The filtration unit requires about one kW of power to operate and cleans about 1500 cu metres (53000 cu ft) of air per hour within the airlock. It is possible to buy particle counters from upwards of £300, but typically circa £2000, to validate how effective the control measures have been.

The temporary airlock also helps to control dust which can enter when the external doors are opened. We have experimented with providing a vacuum table station where items/clothing being carried into the room can be cleaned. The vacuum tube is serviced by the main airlock filtration system. In operation we found this approach effective but needs policing to ensure workers use it. Providing a small translucent vortex unit and dust container at the vacuum station gives a low cost overt demonstration to both workers and management.

When the construction activities are complete we can knock down and remove the airlock, or if desired incorporate it as a permanent feature of the room. The construction of the unit has to be robust to support the weight of heavy equipment which may be wheeled over it. The air handling of the temporary airlock is self contained, avoiding the need to modify the permanent air handling and avoiding making any new holes in the fire resistant wall.

For those who want to experiment with this technology, here's one low cost approach using a kit:

 In the USA you might want to look at the Oneida range of vortex units, for example the Dust Deputy. We used vortex devices made from steel to be able to withstand the rough environment on a construction site. They are more expensive, but do a good job. When using this technology around servers or network equipment be sure to use anti-static counter-measures and good electrical grounding. The swirling dust in the air flows can create a hefty level of static electricity.

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