Thinking inside the box

Published: 8-Mar-2017

When designing a cleanroom, it is natural to focus on aspects such as hygiene, air cleanliness, thermal performance and control of temperature, pressure or light. But what about the external potential? Richard Alston, Kingspan Cleanroom Systems, argues that optimisation of space and ease of maintenance should also be considered and could deliver far more value

A walkable cleanroom ceiling can provide considerable practical benefits, offering a neat solution for storage and supporting the cleanroom’s often-extensive mechanical services. In addition to offering faster installation and often removing the need for secondary steelwork, it also creates a straightforward access route for both installers and maintenance personnel.

There are two key considerations when selecting the right materials to construct a walkable cleanroom ceiling – structural strength and fire performance. The traditional panel core options for cleanroom construction, such as polyisocyanurate (PIR), Mineral Fibre and Aluminium Honeycomb, can all be used to create a walkable surface, but they are not without their disadvantages. However, as research and development into insulation technology has expanded, a solution may now be found in a new hybrid core.

Why walkable?

The standard for the design, construction and start-up of cleanrooms and associated environments, ISO 14664-4, advises that all services should be “designed, located and installed such that the cleanroom is not compromised by contamination.” By ensuring that the lighting systems, HEPA filters and other controls are accessible from the interstitial space above the cleanroom, the need for workers to enter the controlled environment when conducting maintenance or making modifications is removed.

There will be no need to stop production, clean and re-sanitise the area every time there is a mechanical issue or routine checks are made, reducing cleaning costs and production downtime. Consequently, more regular inspections of the cleanroom’s performance can be conducted. This can extend the lifespan of the unit and safeguard the health and safety of both internal and external staff.

However, walkable is not the same as non-fragile. While a surface may be perfectly able to bear the weight of a maintenance worker, if it is unexpectedly overloaded with additional machinery, people or the increased point load of a worker tripping and falling, it is likely to give way.

Aside from the serious injury or loss of life that a fall from height can cause, an incident of this kind could also be devastating on a business level. In April 2008, the Corporate Manslaughter Act and Corporate Homicide Act came into force in the UK. This legislation means that companies and organisations are held fully accountable for any serious failures in the management of health and safety, and may consequently be subject to huge fines and even imprisonment.

Much of the responsibility ultimately comes down to the enforcement of safe working practise in the day-to-day running of the facility – e.g., having clear signage and training to ensure the ceiling platform is only used for occasional activities such as inspections, minor repairs and cleaning and not as a permanent work space. However, the fundamental design and construction of the cleanroom is also a central consideration to reduce the risk.

Structurally sound

The UK Health and Safety Executive (HSE) investigations into incidents concerning insulated suspended ceilings identified that they are often caused by inadequate ceiling designs, and design loads that are not representative of the installation and maintenance activities that take place.

In accordance with BS EN 1991-1-1, the different types of loads that the cleanroom ceiling is likely to be subjected to all need to be taken into consideration. This includes the dead load of the construction itself and imposed loads such as maintenance activities. This highlights the need for close collaboration between the designer, project engineer, manufacturer and end-user to accurately determine what loads the walkable ceiling can and will need to bear, and therefore the best materials and designs for the job.

While the emphasis often lies with selecting the panel core with the best tensile strength, it is important to avoid the trap of the “single-element approach”. In 2010, the HSE investigated a fatal accident where two men fell through the ceiling of a frozen food store. It discovered that the insulated panels separated from the supporting steelwork due to failure of the bolts that secured them to the frame.

Rather than relying solely on the strength of a single component, a more holistic approach which views the panels as part of a wider cleanroom system, including the fixings, coatings and other details, is necessary to create structurally sound walkable ceilings that will stand the test of time. This is especially important in a cleanroom environment because, as explained in the HSE’s Action Statement released in reaction to the incident detailed above, “[e]nvironmental conditions may cause deterioration of ceilings or their supports, making them incapable of carrying loads”.

In extension of this “system-approach”, incorporating fall-prevention equipment (such as handrails), edge protection and boarded walkways to distribute the weight into the initial design of the cleanroom can also help improve the safety of a walkable ceiling. Aside from the obvious safety benefits to the workers once the facility is up and running, including them in the design from the beginning ensures that the dead load of the construction, and therefore the potential additional load-bearing of the ceiling, is accurate.

The burning issue

It is one thing to ensure that a structure is safe to walk on, but will the selected material also perform in the case of fire?

Fire safety is an imperative consideration for any construction project, but it is particularly important in a cleanroom environment where dust particles can compromise its performance and damage processes. The level of fire resistance needed varies with the specific application, however choosing a construction material that does not self-propagate fire is key to protecting the cleanroom. A material that carries FM Approval offers additional peace of mind, as it has not only been rigorously and independently tested, but will also meet any insurance requirements.

Although a fire within a cleanroom that uses fire-resistant interior wall and ceiling panels will be small and contained, if the products being manufactured within it are smoke-sensitive, the physical and financial damage could be considerable. In these types of environments, it would be advisable to choose a product that meets the standards of FM 4882 Class 1 Interior Wall and Ceiling Materials or Systems for Smoke Sensitive Occupancies. This certifies that the material not only restricts the spread of the fire, but also limits the production of smoke.

Core options

There are numerous core materials that can be chosen when specifying a walkable ceiling. The selection of which is often a balancing act between spanning requirements and fire performance.

The most popular choice has often been Aluminium Honeycomb, which provides both superior load-bearing and fire performance properties. However, it costs roughly three times more than other systems and requires much more steelwork, adding to the installation time and increasing capital costs. It is also more difficult to make alterations or add to the construction once it has been erected.

As insulation technology develops, new solutions are now available on the market that tick all the boxes, without the high costs associated with Aluminium Honeycomb. Hybrid closed-cell insulation is being increasingly specified for constructions which require an especially high level of performance and walkability.

The panels can achieve U-values as low as 0.08 W/m2•K, depending on the panel thickness, and are ideal for walkable ceiling constructions thanks to their good shear and tensile strength. Some kinds of closed-cell insulation panels can achieve a Euroclass fire rating of B-s1,d0 to EN 13501-1, the best possible rating for hybrid closed-cell insulation. Able to achieve FM 4882 Approval, these panels are also suitable for smoke-sensitive environments, making them ideal for pharmaceutical manufacturing, food preparation or similar industries.

Both the traditional and newer materials are available from manufacturers as a complete system, including fixings, coating options and even fall protection equipment. This makes following a holistic design process easier, as all the products are designed or selected to work together. From a performance perspective, this has obvious benefits for ensuring the construction envelope is airtight, and any joints are integrated and flush. However, it also offers assurances that all the components supporting the panels can bear the loads the cleanroom is designed to support.

The design and construction of a cleanroom will ultimately be led by the fundamental requirement to create a controlled internal environment. However, by considering the space around the cleanroom as a part of the system, it is possible to create a facility which not only performs to the highest possible standards, but also is easy and safe to maintain in the long term, offering greater value for money.

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