Twelve things that should no longer be seen in cleanrooms

clean room example

Twelve things that should no longer be seen in cleanrooms

Over the past few years I have walked through many different clean rooms, both old and new, designed and built by the small operators and the blue chip multinationals.  Regretfully, a common thread with a lot of these facilities are frequently very poor design choices.  Often they are not in direct conflict with any standard or regulation, however they can pose a significant risk to your cleanroom’s long term compliance. With the pending Annex 1 revision of the code of Good Manufacturing Practice on its way, it would be help to draft a few points to consider and for me, the twelve things that should no longer be seen in cleanrooms!

1. Surface issues

Where starting and primary packaging materials, intermediate or bulk products are exposed to the environment, interior surfaces (walls, floors and ceilings) should be smooth, free from cracks and open joints, should not shed particulate matter and should permit easy and effective cleaning and, if necessary, disinfection.  Section 3.9 PE009-8 – PIC/S Guide to Good Manufacturing Practice Part 1


The internal skin of your cleanroom is your primary barrier that keeps the good things in and the bad things out.  Like your own skin, it should be well maintained and only pierced if absolutely necessary.  In addition holes, bumps, cracks, sharp corners and raised surfaces all create cleaning headaches.  Think of the effort required to clean a large sheet of glass versus a brick wall.  The following will provide common examples where the integrity of the internal skin of your cleanroom has not been respected.

2. Rivets

Rivets are used to fix in place coving or window frames or even to join panels.  They are necessary in certain circumstances, but completely unnecessary most of the time.  At best they are presented as a lump with a smear of silicone over the top and at worst a hole directly into a stagnant, uncontrolled part of your facility.  A rivet is fine if it is behind a flashing or coving, but it should never be seen on the internal surface of an operational cleanroom.  There are a number of properly engineered solutions that are more effective in terms of cost, time of installation and appearance.

3. Mushroom bolts

A mushroom bolt is used to hold up a sandwich panel ceiling.  A hole is drilled right through the ceiling panel, a threaded rod is pushed through and is fixed to the roof.  On the clean side of the ceiling a disk shaped like the top of a mushroom is screwed on, holding the sandwich panel in place.  So why don’t I like them?  Again, because there are perfectly suitable alternative solutions that don’t involve drilling a hole straight through your internal cleanroom skin.  Many good cleanroom contractors have proper, concealed fixings that don’t break the cleanroom barrier and still give you the strength of a mushroom bolt.  If you have them already however, I would leave them as they are; retrofitting a concealed ceiling hanger is simply not possible.

4. Grey electrical conduit running down the wall

Imagine you have just built the most beautiful cleanroom, but the security works are under a separate contract.  The security firm walks in and with horror you see them start whipping out ¾” grey conduit and start screwing it into your beautiful, flawless cleanroom wall.  I see this a lot, to the point that it is now a bit of a running joke.  To be honest it happened to me once early in my career.  Whether you are working with sandwich panel, stud and plaster/drywall or blockwork, with proper forethought, all services can and should be concealed.  In addition, proper project communications and a good specification should help to minimize these types of situations.

Practical considerations:

These design features are often considered cleanroom best practice, but often lead to cleanrooms that are more difficult and or expensive to maintain than they should be.

5. Windows with a sloping sill

I know that this is even specified in some regulations, but frankly these days a modular, gas filled double glazed window unit that sits completely flush to the surrounding will not destroy your budget if used wisely.  If your cleanroom window looks into a non-cleanroom space, then install a single pane flush to the cleanroom side and offset the cost of the double glazed ones.  If this doesn’t change your opinion of them, then watch how long it takes your cleaning staff to properly clean a single glazed window with a sloping sill, then see how long it takes to clean the equivalent area of wall.  Then take that time and multiply it by the number of windows you have in your facility and the number of times you clean your facilities every year.  The operating costs of your cleanroom will stay with you longer than the memory of having to find a little bit more in your new cleanroom budget.

6. HEPAs in ISO 8 / Grade D cleanrooms

It’s a common misnomer that it’s not a cleanroom if it doesn’t have a HEPA filter up on the ceiling.  To some people HEPAs have magical properties that transfer a standard room into a high tech facility.  Remember that a Grade D / ISO 8 cleanroom is specified in terms of the particle load of the air, not how this particle load is achieved.  A properly designed HVAC system will easily delivery Grade D / ISO 8 air without HEPA filters (and with less than 20 air changes per hour by the way).  These systems are significantly cheaper, use far less energy and are much simpler to initially certify and keep certified.

More thought should be given to the strategic placement of HEPAs on the return of a Grade D / ISO 8 HVAC system, than the supply.

7. Completely sealed doors

As cleanrooms operate at an elevated pressure, there is often a concerted effort made to make the rooms as tightly sealed as possible.  This can cause you a lot of pain getting your facility properly pressure balanced at commissioning and over the long term trying to keep it in specification.  A reasonable amount of airflow under a door will make your pressures more static, will reduce stress on the facility as you open and close doors, and will keep it in specification for longer.  This has to be balanced of course with minimising your cross-contamination risk and making sure that you do not lose too much of the conditioned air that costs you so much money to produce.  Some air conditioning systems perform better in terms of pressure control than others, so take this into consideration as well.

Appearance is everything:

Even though it is a functional industrial space, it is vital that a cleanroom looks good.  A good looking, well finished cleanroom shows that you are under control. It inspires confidence in your auditor rather than inspiring them to gown up and head into your facility with a magnifying glass.

7. Bad silicone sealant application

There are many types of bad silicone sealant application, some worse than others.  Applying silicone is an art, and watching a true professional seal up a cleanroom is a joy.  However it is a skill that with guidelines and a bit of patience, any competent tradesman can master.  Here are some tips:

  • Only apply silicone in a clean environment – Dirt trapped in silicone will make your cleanroom look dirty forever.  Make sure that all surfaces have been wiped clean, with no traces of cleaning materials or solvents.  If you are using a polyurethane sealant, then you will need to keep the room clear for at least 24 hours after application, as it takes a lot longer to form a “skin” than silicone sealant.
  • Poor silicone application to sandwich panel joints – When filling a gap like a join between two panels, silicone is applied in a long sweep along the joint.  A moistened towel or cloth is then run down the joint to remove the excess.  Often, too much silicone is removed and you are left with a gaping chasm in your wall or ceiling that you will curse forever.  There will be a slight dip across the join which occurs due to the surface tension of the material, but it should be no more deep than the gap is wide.
  • Smeared silicone – Smeared silicone doesn’t just look bad, it will peel off over time and create a potential contamination issue.  It is worthwhile discussing with your cleanroom installer what is an acceptable silicone application and what is not;
  • Improperly matched silicone colours – At the risk of sounding like a colour consultant, improperly matched silicone with your paint or sandwich panel can ruin your perfectly applied finish.  Pure white silicone applied to off-white sandwich panel is a perfect case in point.  Any slight imperfection in the sealant application will stand out markedly against a darker backdrop.  You want your cleanroom wall to look as homogenous as possible, as any changes draw in the eye and highlight any imperfections.


8. Not enough light

A dull cleanroom will cause you many problems.  Contamination becomes easy to miss when cleaning, mistakes are made when reading instruments, and like a moth is drawn to light on a warm summer night, so is an auditor drawn to a dark, shady space, to see what type of non-conformance might be hiding in there.  Cleanroom lighting should be uniform throughout, with minimum shadowing dark spaces.

9. Too much light

Often I enter a cleanroom and immediately have the urge to reach for some sunglasses.  While a well lit cleanroom does look good, it can cause a range of issues, and not only glare and excessive heat loads.  The main problem is that it competes for space with your HVAC registers.  Despite what some architects and interior designers will tell you, in a cleanroom optimal location of your HVAC registers are far more important than where your lights go.

Basic problems:

These are the no-brainer problems that should be obvious, but I keep finding in cleanroom.  What it demonstrates is that the designers have not understood the basic concepts of cleanroom design.

10. Things that poke into clean environments

If you want to pass material from a Grade C room into a Grade B room through a Pass Thru Box, into what space should the Pass Thru protrude?  The Grade C space should be the obvious answer, but time and time again I see the Pass Thru protruding into the Grade B space, either half way or fully.  Your critical areas should be as close to a smooth, six sided box as possible.  This enhances airflow, reduces dead zones, coving, joins and sealing and makes the space quicker and easier to clean.

11. Smoke detectors

Cleanrooms are designed to remove particles from the air as they are generated.  These particles can be general dirt, product, raw materials or even smoke.  When you consider this, why on earth would anyone mount a smoke detector for fire protection on a cleanroom ceiling?  Yet I continually see these specified.  They are a necessary part of your fire detection arsenal, but should be located in places where any smoke generated is likely to find them.

12. Internally insulated ducting

The internals of your ductwork and your AHU, like your cleanroom walls, ceilings and floors should be smooth and impervious.  Therefore internal insulation or sound proofing has no place in cleanroom duct work.

Internal insulation, particularly the cheap and nasty stuff, will shed fibres that will shorten the life of your HEPA filters, or blow directly into your cleanroom.  In addition, inadvertent or long term contamination of your ductwork with raw materials or product will give you a massive cleaning problem.  If you have a serious micro or mould issue, then replacement of the ductwork may be your only option.

What to do next:

There are certain things that are simple to fix, such as replacing riveted covings and dodgy silicone work.  Holes in your cleanroom internal skin, particularly if you use a sandwich panel, can be difficult to fix, unless you are prepared to spend a bit of money.

This highlights the importance of getting it all right first time and using the right people from the start.  There is an easier, cheaper and less risky path on all cleanroom projects.  I hope that this document, the twelve things that should no longer be seen in cleanrooms, will give you some of the right directions to follow.

Other posts about clean rooms:

A basic clean room

Clean rooms explained in simple terms

15 things you should never see in a clean room

What is your clean room costing you?

Optimising your clean room – getting QA buy in to down time

Now you know it all! Take the clean room quiz.

(3) Comments
  1. I cannot imagine how many contractors and owners will be saved from current practice, say even best practices which in fact has flaws. Now, by your thoughtful contribution you create a flawless world, to remember that it relates to a highly critical human endeavour, the cleanrorm operation, the injectables.or the electronic industry.
    No words are adequate to express the gratitude we owe you.
    Hoping that the readers could also contribute and add to your list.
    Kind regards,
    v. surjana

  2. Informative blog. How much relevant is to have epoxy flooring over radiant heated flooring.

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