CLEANROOM TECHNOLOGY

February 2020Revision 1

ABN Cleanroom TechnologyCopyright

WHITEPAPERRELIABILITY BOOST IN PRE-ENGINEERED CLEANROOMS WITH FAULT TREE ANALYSES

Kieleberg 13740 Bilzen, BelgiumT.: +32 (0)89 32 10 80www.abn-cleanroomtechnology.comwww.stericube.com

How to apply the right maintenance strategy, based on failure mechanisms in relation to the criticality of the cleanroom system and its components.

168| WHITEPAPER OVERVIEW

127| FIRST IDENTIFY, THEN ASSESS

106| FMEA, OR HOW DO YOU GAIN INSIGHT INTO POTENTIAL FAILURE MECHANISMS?

85| FTA IN PRE-ENGINEERED CLEANROOM DESIGN

74| HOW TO UNDERSTAND FAILURE BEHAVIOUR?

53| WHAT’S NEW WITH RELIABILITY ENGINEERING AND ASSET MANAGEMENT?

42| ‘DESIGN FOR RELIABILITY’ TO UNDERSTAND A CLEANROOM’S FAILURE BEHAVIOUR

31| INTRO - RELIABILITY IN PRE-ENGINEERED CLEANROOMS

CONTENT

RELIABILITY BOOST IN PRE-ENGINEERED CLEANROOMS

WHITEPAPER

18WANT TO KNOW MORE?

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APPLY THE RIGHT MAINTENANCE STRATEGY, BASED ON FAILURE MECHANISMS IN RELATION TO THE CRITICALITY OF THE CLEANROOM SYSTEM USING FAILURE ANALYSIS TOOLS.

RELIABILITY IN PRE-ENGINEERED CLEANROOMS

INTRO

Imagine the possibility of telling you now about future problems with your

assets or processes. Ever thought what you would be willing to pay for

that type of foresight? Quite an investment for sure. Of course, you can sit

around and wait for something to go wrong. Or not. That’s up to you. You

can as well anticipate problems before they happen and reduce the risk

of failure. That is what Failure Mode Effect Analysis (FMEA) and Fault

Tree Analysis (FTA) can do. They help identify potential issues with your

assets before they happen. In this whitepaper, you will learn about the

necessity of understanding failure behaviour and failure analysis from a

pre-engineered cleanroom design approach.

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‘DESIGN FOR RELIABILITY’ TO UNDERSTAND A CLEANROOM’S FAILURE BEHAVIOUR

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WHITEPAPER

Both reliability and availability are well-known terms in the field of cleanroom technology. They are in fact closely related to each other in the design phase of a cleanroom. This so-called ‘Design for Reliability’ is a fundamental starting point for all cleanroom environments since every cleanroom must meet the requirements according to the function they are designed for and this on a 24/7 basis.

However, other than the design phase, reliability is also closely linked to availability in the operational phase of the cleanroom: reliability is the ability of the entire cleanroom system to perform according to a required function under given conditions for a given time interval. After all, designing a cleanroom system for unlimited conditions is impossible.

In order to measure the reliability performance and to determine whether reliability requirements of cleanroom designs are met, you can apply the Survival Probability: the proportion of units that survive longer than a specified time.

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WHITEPAPER

Since a cleanroom has to be considered at all times as a critical asset that must guarantee its function day in day out, there is a 1-on-1 connection between availability and reliability, as we explained earlier. Opposed to those critical cleanroom assets or systems, there might as well be assets that are in need of high availability during weekdays only (which is the production period), and can be maintained or repaired at the weekend (the non-production period).

Let’s take following case: a VIX cleanroom with a night setback can lower the Air Change Rate during non-production periods, but the pressure cascade must achieve the predefined values at all times. Even during non-production hours, the function of the cleanroom -or at least a part of the defined user requirements- must be achieved at high reliability level.

RELIABILITY BOOST IN PRE-ENGINEERED CLEANROOMS

WHAT’S NEW WITH RELIABILITY ENGINEERING AND ASSET MANAGEMENT?

This however, is not the case with cleanrooms, meaning that ‘production time’ requires an approach that’s totally different from ‘availability’ in the field of cleanroom design.

An accurate understanding of the cleanroom’s failure behaviour is therefore of key importance. How to apply the right maintenance strategy based on those failure mechanisms in relation to the criticality of the cleanroom is the question one should ask.

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Reliability can be framed within the bigger concept of ‘reliability engineering’ in which the well-known FMEA and FTA are solid methods used to find failure modes and map their effects. The concept of reliability engineering itself must be approached as a part of asset management in relation to the line of sight.

This means that reliability engineering should better be seen as the connectivity between the strategic goals of the company and the on-the-ground daily activities, such as operations, performance and planning. Reliability engineering and failure behaviour are perhaps the most underestimated subjects in cleanroom design. For this reason, we chose to focus on reliability and failure behaviour in pre-engineered cleanroom design in this whitepaper.

WHITEPAPER

Our previous whitepaper ‘5 forces that drive energy efficiency in pre-engineered cleanroom design’ discusses the force Air

Change Rate in cleanroom environments more thoroughly.

Get free access to this whitepaper

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WHITEPAPER

There are multiple methods to perform risk analyses related to dependability in critical environments. We are familiar with following tools: FMEA (Failure Mode and Effect Analysis), FMECA (Failure Mode Effect & Criticality Analysis), DRBFM (Design Review by Failure Mode), FTA (Fault Tree Analysis), ETA (Event Tree Analysis), HAZOP (Hazard & Operability Studies), HACCP (Hazard Analysis and Critical Control Points) and RBD (Reliability Block Diagram).

RELIABILITY BOOST IN PRE-ENGINEERED CLEANROOMS

HOW TO UNDERSTAND FAILURE BEHAVIOUR?

In the next coming parts of this whitepaper, we’ll focus on 2 relevant tools in order to achieve reliability in cleanroom design. 2 tools that are most applied in reliability engineering and considered as techniques for identifying risks:

The FTA tool: a top-down methodology

The FMEA tool: a bottom-up strategy that is less structured and requires more expertise

Both FMEA and FTA are extremely powerful tools to bring reliability to a higher level in cleanroom design. However, thoroughly performing a FMEA or FTA from scratch cannot be underestimated, it is intense and time-consuming work with risk of human mistakes.

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FAULT TREE ANALYSIS IN PRE-ENGINEERED CLEANROOM DESIGN

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WHITEPAPER

Let’s start with explaining a Fault Tree Analysis in more detail. FTA is a widespread deductive and top-down method to investigate cleanroom failure behaviour and determine system dependability. It is a method where a general system state is decomposed into chains of more basic events of components. The logical connections or relationships between events and their causes are described analytically in a reliability structure, presented by a fault tree visualisation.

A fault tree is a logic diagram that represents the connections between an event and the cause of the event (typically component failures). The commonly used logic AND/OR-gates visualize how the component states relate to each other and to the state of the system as a whole. There are several types of events to be distinguished in FTA: a top event, basic event, undeveloped event and conditional event.

A deductive method in the context of FTA means that the analysis starts with a top event, a cleanroom system failure. The flow goes backwards from the top of the fault tree towards the leaves of the tree to determine the Root Cause Analysis (CRA) of this top event.

The outcome of an FTA will clearly show how various component failures cause a cleanroom system failure. After finalizing the FTA, two levels of analysis can be distinguished: a qualitative and quantitative analysis level.

With the former (qualitative level), the fault trees are reduced to Minimal Cut Sets (MCS) in order to create the smallest combinations of basic events that are required to cause the top event.

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WHITEPAPER

With the latter (quantitative level), the probability of the top event’s occurrence and other quantitative reliability indexes are calculated mathematically in order to determine the failure rate or probability of a system component, like e.g. a pump. The qualitative FTA can be extended into a quantitative FTA by adding quantitative information of component reliability. Such a quantitative FTA can be used to determine the reliability of the system using Boolean algebra.

The output of the quantitative analysis level indicates the reliability of the system and provides insight into which elements of a cleanroom system are more critical than others or rather less critical than others.

Unneeded components are left out whilst only those components with a high failure rate are included in spare part management. This allows you to take into account the redundancy aspect in function of the reliability of the system.

RELIABILITY BOOST IN PRE-ENGINEERED CLEANROOMS 9

One of ABN’s VIX cleanrooms with redundant design for minimal system failiure.

FMEA, OR HOW DO YOU GAIN INSIGHT INTO POTENTIAL FAILURE MECHANISMS?

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WHITEPAPER

Next to FTA, we will be discussing FMEA as well in more detail. FMEA stands for Failure Mode Effect Analysis. This means that we examine (Analysis) to what degree an installation can fail (Failure Mode) and what the effect of failure (Effect) will be. Shortly said, an FMEA identifies unacceptable failure behaviour, evaluates it together with their effects and prioritizes the risks associated with those potential failures and effects of those failures.

So, an FMEA is a tool that allows us to examine what can possibly go wrong in the process or product in order to take constructive measures in advance with the aim to reduce the risk of errors, reduce the impact of errors or even prevent errors.

FMEA is a qualitative bottom-up inductive technique with regard to the failure symptoms of the system’s components and can be extended to a quantitative FMECA by performing criticality analyses. Information about the consequences and effects of the failure is usually collected through interviews with experienced people with different knowledge.

This tool helps you to avoid costly changes through early identification of component failure and to guarantee higher uptime. A thoroughly executed FMEA provides insight into potential failure mechanisms and is expressed by a Risk Priority Number (RPN), a numeric scale that ranges from 1 to 1000. Potential failures and their associated effects are rated on three scales: severity, occurrence and detection.

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WHITEPAPER

The RPN is a function of the severity of the failure, the likelihood of it occurring and the ability to detect it before it happens. In case that the RPN has an unacceptably high value -in combination with a risk matrix, the red area- certain control actions are needed.

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FIRST IDENTIFY, THEN ASSESS 7

WHITEPAPER

We need to get a clear understanding of the cleanroom as a system fi rst. Starting from a cleanroom system failure as an undesired top event, all possible functional failure modes are identifi ed by means of a system level FTA analysis. The fault tree is performed on all subsystems (cooling, heating, ventilation…) to fi nd out how they relate to each other. Subsequent to this FTA analysis, the most critical functional failure mode is determined via a system level FMEA.

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The outcome of performing a system level FTA is the identifi cation of a set of failure modes. Using FMEA, the criticality of those failure modes is assessed. So, fi rst identify the failure modes, then assess the criticality. To analyse the failure behaviour of a cleanroom system, three levels of failure are determined: a system level, a function level and a component level.

Let’s see how that works for our modular & pre-engineered cleanroom concept VIX.

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Example of system level FTA

After performing the function level FTA of the AS-IS situation, we use FMEA for fault trees with many OR-gates to determine which component failures modes have the highest criticality. The failure modes with the highest RPN value are further optimized to lower the value (RPN = severity x occurrence x detection).

Then, starting from the most critical functional failure modes, the corresponding component failure modes are identifi ed by means of a function level FTA analysis. Thereafter, the most critical component failure mode is determined via a function level FMEA.

In some cases it may be necessary to perform a more in-depth analysis at component level. This then determines the corresponding failure mechanisms of each component failure mode. The most critical failure mechanism (e.g. pump cavitation) is determined by means of an FMEA. These fault trees clearly show where the criticality of the system can be found.

WHITEPAPER

Let’s focus on the analysis on function level. Perform a function level FTA of the AS-IS situation fi rst. The FTA analysis of the most critical function failure modes can have AND and/or OR-gates.

RELIABILITY BOOST IN PRE-ENGINEERED CLEANROOMS 13

Example of system level FMEA for temperature failure

Fault trees with multiple AND-gates have a low RPN value and show high redundancy and reliability. Fault trees with many OR-gates are more likely to fail and further optimization is necessary depending on the User Requirements Specifi cations (URS).

As we’re going towards the TO-BE situation, we perform a new function level FTA. Component failure modes with the highest criticality can be optimized in several ways:

WHITEPAPER

Redundancy: a new TO-BE FTA analysis shows more AND-gates that reduce the risk of failure in critical function failure modes.

Using more reliable components to reduce the risk of system failure.

Spare part management and increased serviceability for those components that cannot be performed redundantly but influence the critical function.

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Example of function level FTA for temperature failure

RELIABILITY BOOST IN PRE-ENGINEERED CLEANROOMS 15

WHITEPAPER

Ultimately, a new TO-BE function level FMEA of the component failure modes is performed to confi rm the enhancement of the RPN value. Here below, you can fi nd some potential failure modes of our VIX cleanrooms, for which actions have been taken to lower the RPN value.

Example of function level FMEA for temperature failure

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WHITEPAPER

So, after reading this whitepaper you can imagine that when you have to start FTAs and FMEAs from scratch every time again, it requires an enormous time spending. That’s exactly the reason why they are often not performed thoroughly or even not at all. A missed opportunity, because these failure analysis tools learn you how to apply the right maintenance strategy, based on failure mechanisms and in relation to the criticality of the cleanroom system or its components.

WHITEPAPER OVERVIEW

Being ABN Cleanroom Technology, we approach FMEA and FTA from a pre-engineered idea that allows us to compose building blocks in order to increase the reliability in cleanroom design. From an embedded modular and pre-engineered design point of view, a FTA or FMEA needs to be set up only once instead of from scratch every time.

Therefore, it is absolutely necessary to continue with a modular & pre-engineered cleanroom design approach in order to thoroughly apply these valuable tools to understand the failure behaviour of your cleanroom system. Due to VIX, our redundant cleanroom system ensures that nearly no system failure occurs.

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Souce: Peeters, Basten & Tinga. (2017). Improving failure analysis effi ciency by combining FTA and FMEA in a recursive manner.

RELIABILITY BOOST IN PRE-ENGINEERED CLEANROOMS 17

WHITEPAPER

WANT TO KNOW MORE?

Jo NelissenCEO/Founder

Mark HammeneckerSales Manager Cleanrooms

Kieleberg 13740 Bilzen, BelgiumT.: +32 (0)89 32 10 80

www.abn-cleanroomtechnology.comwww.stericube.com

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Jo Nelissen MSc is the founder and CEO of ABN Cleanroom Technology and holds a Master Degree in Mechanical Engineering & Asset Management. He focuses on innovative concepts in pre-engineered cleanroom design. Furthermore, he specializes in asset management in modular & pre-engineered cleanroom design.

Mark Hammenecker holds an Electronics and Communications Engineering Degree and is responsible for the french branch of the cleanroom sales team. Mark has particular expertise in cleanroom maintenance management. Due to his years of experience, he contributes actively as expert in the field of cleanroom maintenance and is member of multiple maintenance associations.