Cleaning a Cleanroom

STEVEN CLEMENS

Cleanroom cleaning - what to do? Steven raises a few issues that will help you ask the right questions before committing yourself to a cleaning company.

We spend millions of dollars on creating the cleanest environment we can, on air handling equipment, HEPA or ULPA filters, on the design of the room and equipment. How much thought goes into cleaning the room from the design stage, from construction to start up, to an ongoing cleaning program.

Do we just trust our contractors or suppliers, or do we implement our own systems, and validate our own cleaning protocols.

What contaminants are we concerned about?

1. Particles or Fibres
2. Micro-organisms or pyrogens
3. Static Electricity
4. Chemical residues or outgassing

What levels of contamination are we concerned about, what limits or tolerances do the product or services require?

It is important from the outset to establish which areas are to be kept clean and at what level. So initially it is crucial to define the critical and general zones within the room and then work out what contaminants and levels are acceptable within these zones, what levels exist now. You will need to monitor and test your environment to determine this, i.e. particle or microbial counters, settle plates or membranes, static field monitors or gas and chemical sniffers.

This will give you some ideas on the frequency of cleaning needed, it maybe hourly, daily, weekly, monthly, quarterly etc., set up a cleaning program and schedule. Whatever needs to be done at these intervals must be documented and make your cleaning staff sign on your cleaning record exactly what they did, when they did it and what approved products they used (any observations from the staff must also be noted).

The timing of the cleaning process is vital. Many tests have been done proving contamination levels sore when cleaning is actually being done, so timing is critical. How long after the cleaning process is performed will contamination levels go down and be acceptable? You need to work this in with your production times, some plants operate 24 hours a day seven days a week, to determine when production can either be stopped or at least are their less critical times during production.

Who should clean?

We have personally found you are better to use your own cleanroom operators, they know the equipment, the room and what is critical and what is not. Some outside contractors who specialise in cleaning cleanrooms are also an advantage. But your run of the mill commercial contract cleaner sometimes does not even know what a cleanroom is, and as soon as you turn your back they are using their favourite Chux or cotton mop.

What products should you use?

Determine what cleaning methods you need to use. Will you use water or just dry methods, or a combination of both, do you need to disinfect or sanitise surfaces, or treat with antistatic solutions.

Vacuum systems for floors and other surfaces are great at removing particles greater than 100mm, but for particles of 10mm and smaller they are only 10% efficient. A dry wiper is great at moving particles and microorganisms from one side of the bench to the other, or just pushing them into the air, some also create large static charges

Through our experience, it is best to use a combination of both wet and dry methods, for floors, benches and equipment. The wiping or mopping material needs to be wet, this attracts particles to it and therefore is better at removing particles from the surface. A non-ionic or Cationic (is better for controlling static) detergent when diluted with water is even better. They further reduce the surface tension that holds particles to a surface.

You need filtered water or solutions e.g. Ethanol, Iso Propanol, not tap water. If you are sanitising surfaces you need to look at contact time, most alcohols evaporate in less than 30 seconds and so a microbial inhibitor can help like Trichlorosan or Chlorohexidine. Some tend to leave a film depending on the amount added to the alcohol.

Phenol's and Quats are better to be used on floors and walls as they can be corrosive, and should be rotated on a regular basis to reduce the chance of resistant strains of microorganisms developing.

Wipers and mops

There is no one wiper or mop that will suit every situation, they are different. A rule of thumb with disposable wipes is the absorbent ones tend to shed the most, and the ones that don't absorb solutions well, shed the least, so it becomes a trade off.

Reusable wipes or mops tend to shed least and absorb the most, depending on the material. PVA is the most absorbent but tends to rip and tear when dry. Bacterial growth problems arise when you try to keep it wet, and they also absorb a large amount of chemicals when being laundered, which are hard to remove.

To choose your cleaning products, get a range of materials from different suppliers, and then test them. See what best works, different applications require different products and you will not find one product that can do everything.

Summary

If you are building a new facility, design it around making it easier to clean. If it is an existing facility do an audit on what you do now, what your use is, is it acceptable, what contaminants and at what levels are you concerned about, do you meet these requirements. If not, re-evaluate your cleaning schedules and programs, and equipment and products.

Cleanroom Clothing Performance

Robin Howie

Robin Howie Associates, Edinburgh

Robin concludes his two-part article (for Part 1 click here) with a look at

FACE-MASK PERFORMANCE

As with clothing, face-mask performance is limited by penetration through the materials of construction and leakage between the mask and the body.

One of the standard tests for assessing the performance of surgical masks is the Greene-Vesley test, Greene and Vesely (1962), in which human subjects wearing the mask under test speak a standard set of pronounced words into a chamber connected to a sampling device. This test applied to conventional industrial respiratory protective equipment (RPE) yields surprising results: respirators fitted with exhalation valves can pass this test. As most aerosols pass effectively unhindered through normal RPE exhalation valves, it is clear that the Greene-Vesley test is not a stringent test of mask performance.

More stringent tests for assessing the performance of surgical-masks are therefore required.

Although standard tests for measuring filter penetration and face seal leakage for RPE have been adopted, e.g. European Standard EN 149, (CEN, 1992), such standards tend not to be applied to surgical masks of the types widely used in clean rooms although the standard filter penetration tests described in EN 149 could be applied easily to clean room masks.

However, the standard leakage tests may not be applicable to some masks. With conventional RPE which is intended to prevent the ingress of contaminant, the lower pressures inside the facepiece generated by inhalation can cause some masks to "collapse" onto the face, so minimising leakage. Conversely, with clean room masks which are intended to prevent egress of contaminant, the higher pressure inside the facepiece generated by exhalation may lift the mask off the face, so increasing outward leakage. This effect was utilised in the UK wartime civilian gas mask, which was not fitted with an exhalation valve. During exhalation, an inlet valve on the gas capsule closed and the pressure inside the facepiece forced the facepiece to lift off the cheeks so that the exhalate could escape.

It is therefore possible, particularly for masks with high breathing resistance, that the standard leakage tests intended for industrial RPE, which are based on measuring inward leakage, may seriously underestimate outward leakage.

For assessment of mask performance it is therefore necessary, as with clean room clothing, to rely upon relevant informal tests.

The performance of surgical masks against aerosols has been widely studied. Most such studies have indicated that the performance of surgical masks is poor. For example, Jaakkola et al (1984) reported that the "filtering efficiency of 5 surgical masks was so low that they should not be used as respirators at all", Miller (1996) reported that "up to 82% of the (0.6 - 2.5) mm sized aerosol particles passed through the filters of 9 different types of surgical masks commonly used by dental professionals" Weber et al. (1993) tested 8 different surgical masks and observed filter penetrations ranging from 20 to about 100% for submicron particles. Similarly poor performance has been reported by other authors, (Huff et al, 1994, Chen and Willeke, 1992, Jewett et al. 1992, Nezhat et al. 1987, Portner et al. 1965).

Given the above results and the information on conventional industrial RPE, it is considered that un-valved industrial RPE should offer substantially higher performance than many current surgical masks. However, it should be noted that even for un-valved high performance RPE, it may be necessary to check that inward leakage as determined in the standard laboratory tests adequately indicates outward leakage.

CONCLUSIONS

From the extensive published literature it is considered clear that currently available clean room garments and face-masks are unlikely to offer the level of performance required for high classification clean rooms.

Only clean room clothing for which the manufacturers can supply figures for total protection, particle emission and the potential for generating thermal discomfort or heat strain should be purchased.

Until suitable such data are available from clean room clothing manufacturers and suppliers, studies in real clean room situations are required to determine the real-world performance of clean room clothing and facemasks so that performance and design can be improved if required.

REFERENCES

Particle Counting in Cleanrooms

Richard Howell

Particle Measuring Systems Europe Ltd.

To assess the cleanliness of clean cabinets, isolators, and rooms, the particle concentration larger than a given size is determined by either microscopy (for larger sizes) or an optical particle counter. For speed, cost and statistical validity, assessments are usually carried out with an optical particle counter.

Modern Optical Particle counters provide data in a number of different sizes channels simultaneously which are displayed on an internal screen and may be saved using a built-in printer. Internal firmware often allows procedures such as those outlined in FS209E to be followed simply and easily with a suitable report generated.

Although it is necessary for a clean area to be regularly validated, such validation only indicates the level of cleanliness at a point in time, often when normal (particle producing) operations are not taking place.

Modern clean manufacturing environments often need to be more rigorously monitored to ensure that there is a full and constant awareness of prevailing conditions, including logging episodic events which could be catastrophic if missed. Constant monitoring creates a constant flow of information which results in large volumes of data being accumulated.

A compact approach is to build a disk drive into the particle counter itself. The data can then be down-loaded on to a PC for statistical manipulation as required. Alternatively a lap top PC with a suitable monitoring programme resident could be used, linked directly to the particle counter.

There is an increasing need and desire to monitor more places, more regularly than can be easily achieved using a single mobile counter. This need is being driven by the desire to reduce operational costs, improve production yields and quality, to increase confidence in good manufacturing practices or to fulfil regulatory requirements.

One way of achieving more regular monitoring is to install a Facility Monitoring System.

Computer controlled Facility Monitoring System

A Facility Monitoring System is an arrangement of instrument hardware suitable for making the measurements required which are linked to a central monitoring computer. The computer controls the intake of data from the various devices and logs and displays the information, reporting to the operator any changes in conditions or trends.

The inputs to the Facility Monitoring System may be from numerous sources. In clean areas the optical particle counter data may be transferred to the computer. Alternatively, particle counters linked to scanning manifolds may be installed. The scanning frequency and location being controlled via the PC/software.

If DI water, pure chemicals or gases are used within the Facility their particle concentration may also be monitored by connection of suitable particle counters to the system.

Environmental conditions such as differential pressure, airflow velocity or temperature and relative humidity play an important part in ensuring quality. These may also be monitored using appropriate sensors and the data collected via the PC/software.

Such automated, computer controlled Facility Monitoring Systems will provide increased vigilance whilst decreasing the labour requirements on these activities. If the system is well planned, then a fast detection of potential problems in operating conditions should occur enabling counter measures to be taken rapidly.

Over the longer term any significant trends in operating conditions can be monitored and statistical analysis of data should allow for closer control and identification of normal and abnormal conditions.

Automated Particle Count Data Collection

There are three basic approaches to obtaining automated particle counts:

1. Multiple tubes via multi-port scanning manifold linked to a particle counter

2. Individual particle sensors

3. Combination of manifolds and particle sensors

1. Multiple Tubes- scanning manifold

This is currently the most widely used approach.

Advantages

1. Low cost per point monitored. The system requires the minimum amount of hardware i.e. a particle counter, aerosol manifold and lengths of flexible tubing for up to 30 positions monitored.
2. Low maintenance and calibration costs. Only a single instrument per manifold to calibrate and service.
3. Modern manifold and purge pump systems provide good transportation of particles in 0.1 to 1.0 micron size ranges (i.e. approximately 95%). Typical flow velocities are in the order of 20 meters/sec for standard 10mm lD tubing.
4. Any particle loss for larger sizes is at least consistent thus enabling valid daily comparisons between sample locations.

Disadvantages

1. Can only sample one location at a time. However, sample sequencing may be biased to monitor the most critical locations more often.
2. Loss of particles of 1 micron and greater in the tubes due to sedimentation and impaction may be of importance. These are minimized by maintaining turbulent flow in the tubes by use of purge pumps, no bends of tighter radius that 200min and manifold designs that eliminate valves. Tubing of the correct material and adequately earthed minimises electrostatic attraction problems.

2. Multiple sensors

The use of miniaturised particle sensors at each point of sampling. Typically, the particle sensor will consist of a small enclosure housing an optical system, a light source (laser diode) and signal generation electronics. The sensor will require an external vacuum source and signal communication cable to transmit data to the central FMS computer.

Advantages

1. Sensors will monitor truly continuously and report data to system, therefore detecting short lived particle burst situations.
2. Simple and low cost installation
3. Small and neat design for unobtrusive installation
4. Ease of relocation to alternative positions
5. Provides highest level of confidence

Disadvantages

1. Higher cost per point sampled, each sampling point requires an individual sensor
2. Higher cost of ownership. Each sensor will require calibration and service
3. Sensor to sensor variation due to opto/electronic tolerances.

3. Combination Monitoring

Combination monitoring utilises the advantages of both manifold multiple tube systems and individual sensors. The majority of sampling being monitored with one (or more) manifolds and specific critical locations, continuously sampled by individual sensors.

Advantages

1. Increased data acquisition, especially for critical areas
2. Regular automatic monitoring of background areas
3. Ability to identify episodic events at critical locations, and trend data for background areas
4. Cost effective option

Summary

For automatic particle monitoring the multiple tube and manifold approach normally offers the lowest cost option, however individual particle sensors are being more widely used especially in conjunction with manifold systems. Environmental monitoring or inputs from process sensors 1 may also be easily added.

A well designed, well installed Facility Monitoring System provides a number of benefits to its owners:

1. Increased vigilance
2. Improved Environmental Awareness
3. Higher confidence levels
4. Warning and alarms, both at the computer and if required, locally
5. Documented trend analysis
6. Documented batch reports

A Facility Monitoring System may be installed and augmented as needs and budget dictate. It will provide a flexible yet cost effective quality control management system.

Contamination Control Corner

Hal Smith

What is contamination?

According to the definition given in IEST-RD-CC011.2, ‘A Glossary of Terms and Definitions Relating to Contamination Control’, a publication of the Institute of Environmental Sciences and Technology, a contaminant is, ‘Any unwanted substance present in or on a material or any surface within a clean zone’. This presumes that one is working in an area where cleanliness is regulated. Now we shall examine the types and sources of contamination.

Contaminants are particulate, liquid, gaseous, film or biological. Other authorities also include radiation and electromagnetic interference (EMI) as contaminants. However, this author considers them contamination causes not contaminants. Particles can be solids or liquids and can be solid-solid, solid-liquid, solid-gas, liquid-liquid or liquid-gas as long as they are discrete entities. Films are typically dried liquids containing solids or gasses and are often only molecules thick. A trace amount of gas within another gas may be considered a contaminant. Biological contaminants can be found in all the other contaminant types and are usually only considered when this type of contaminant is suspect.

There are many sources of contamination. The atmosphere contains dusts, microorganisms, condensates, and gases. People, in clean environments, are the greatest contributors to contamination emitting body vapors, dead skin, micro-organisms, skin oils, and, if smoking or wearing cosmetics, the fumes and particles from these materials. Industrial processes produce the widest variety of contaminants. Wherever there is a process which grinds, corrodes, fumes, heats, sprays, turns, etc., particles and fumes are emitted and will contaminate their surroundings. Finally, plants and soils contribute particulate and biological contaminants.

Airborne contaminants may be organic, inorganic, or aerosols, the latter being composites of any number of components. Organic contaminants include hydrocarbons such as hexanes, benzene, alcohols, ketones, and other volatile organic solvents. Inorganic contaminants are mainly composed of gases such as carbon dioxide, chlorine, hydrogen sulfide, sulphur oxides, ammonia, etc. Aerosols can entrain any of the above into liquid or particle agglomerations containing dusts, pollens, small organisms such as mites, micro-organisms, etc.

In addition to dust and other particles (dirticles), surface contamination can be any one of the following - reaction layers of chemical compounds, adsorbed layers of mostly hydrocarbons and moisture, or variable composition contaminants due to preferential diffusion of one component through a substrate.

EFFECTS OF CONTAMINATION

In the microelectronics industry, contaminants cause open and short circuits, epitaxial spikes and many other problems. Disk drive head crashes are caused by contaminants, mainly particulate and film. Optical discs cannot be read accurately if contaminants are present.

In the early days of gyroscopes, particles in the raceways often caused the instrument to seize up. Particles on optical surfaces cause blockages. In an early space flight of a telescope, the scope was to get its orientation by sighting on a star of a certain magnitude of brightness. During the launch, the poorly cleaned instrument released a particle which remained in the scopels vision field. The sun lit up the particle to about the same brightness as the star. As a result, the telescope could not be focused on desired objects.

Outgassing, the release of volatile materials from a material other than by a change of state of the material, is one of the current big problems - not only how to eliminate it but how to measure the propensity of material to outgas. Galvanized materials in an IC fab will cause zinc contamination in wafers. PVC material outgas diethylhexyl phthalates which cloud optics and film on almost all other materials.

Medical facilities must continuously guard against micro-organisms. These organisms are also responsible for shortening the shelf-life of foodstuffs and easily grow in deionized water. Many otherwise clean materials have been compromised by poorly managed storage facilities where heat and moisture have grown molds in packaged materials.

The demand for contaminant-free chemicals and process materials has driven the development of many chemicals with parts per billion or trillion contaminant levels to qualify for use in many processes.

Radiation and Electromagnetic Interference, which includes Electrostatic Discharge (ESD), as stated previously, in the authorls opinion, are not contaminants but produce contamination. White light can change photoresist prior to exposure. ESD can attract particles to an otherwise clean surface, agglomerate particles, and cause particles to be more difficult to remove during cleaning.

If a product is made with poor quality regarding cleanliness issues, the results can be damaging to the manufacturer. Firstly the poor yields mean that the costs of labor, material, and use of facilities is high. Shipping delays and increased inventory occur.

But most important, aside from the loss of profits, consumer confidence is lost and eventually the customer.

Nordic News Åke Möller

HOW GOOD IS CONTAMINATION CONTROL OUTSIDE OF CLEANROOMS?

There are huge areas of modern society, outside of the conventional cleanrooms, that need much better contamination control than they get at the moment. Perhaps the techniques of conventional cleanrooms have a part to play.

Hospital ward conditions need a critical look

In Sweden, approximately 100,000 people get unintentional contaminations in hospital every year and around ten per cent of these become dangerous infections. Now that the research has been done to identify the extent of the problem, it is to be hoped that further research can be directed towards physical measurements that might be taken in hospital wards to reduce these numbers.

Refuse and waste water handlers need protection

Refuse and waste water are produced in enormous quantities in our modern city-concentrated societies and recycling methods become increasingly necessary. The risk of present processes to contaminate workers and surroundings must be evaluated and the contamination controlled.

For a long time now, most countries have been treating their waste water in large open-air plants with aeration methods that can create hazardous aerosols. After treatment to a seasonally varying degree, the waste water is discharged to rivers. In northern Sweden, because of very cold winters, the treatment ponds were enclosed to maintain a reasonably effective temperature but the indoor level of bacterial and chemical contamination was then increasing so quickly that it caused illness among the workers.

For at least two decades, Local Councils have been separating various recyclable items from the general refuse but this has involved closer handling by the workers and has also given rise to more illness.

New Swedish study reveals problems for sewage-treatment workers

Sweden has about 1300 workers in 350 sewage treatment plants. In the south of the country, 15 plants were carefully studied during 1998 and, in 14 of these, there were found to be workers with serious health problems. Among the symptoms described have been abnormal tiredness, skin lesions, headaches, hepatitis, vomiting, diarrhoea, liver cancer, joint pains and memory problems but the specific causes of these symptoms have not, as yet, been identified. Earlier studies had already shown that all new employees, especially the machine operators, were likely to become infected with dangerous bacteria and that electricians working in sewage pumping stations frequently experienced serious problems with their joints.

The results are alarming and the main safety supervisor in one city has called for a check on all 350 installations. There is a big job to be done by cleanroom technology experts

It might be thought that waste disposal areas are not appropriate territory for the cleanroom technology experts who so successfully create extremely clean work areas in factories but these experts know a great number of useful things that are applicable to making very dirty places safe to work in. They know how to create cheap clean air, how to extract risky aerosols, how to avoid creating aerosols. how to use over- and underpressure to isolate risk areas, how to clean and disinfect, and more besides. They have the knowledge to effect improvements if there is the will to put health into the specification. A new opportunitv awaits innovative entrepreneurs who are willing to work out how to apply long-established cleanroom technology principles to very dirty situations. Examples of this are the isolation of contamination sources with walls or clean airflows, extraction of contaminated air at its source, providing clean-air face-masks for the workers and avoiding the aerosol formation that occurs when cleaning is carried out using high-pressure water.

A Swedish contamination control company has recently delivered a protecting airflow device to a London refuse-separation installation. However, most people in the industry are not really aware of the hazards involved and the solutions that are possible.

April Update from British Standards

International Standards

Cleanroom standards being produced for world use by the International Organization for Standardization technical committee ISO/TC209 are progressing. The defined development stages carry prefixes as follows:

WD: Working Draft. Circulation of developing document within the Working Group set up by the ISO/TC209 Committee.

CD: Committee Draft. Circulation of approved Working Draft within ISO/TC209 for approval and or comments by the National Technical Bodies of the participating countries (British Standards Institution in the case of the United Kingdom).

DIS: Draft International Standard. Circulation of the ISO- approved Committee Draft by ISO for public enquiry in all ISO member countries..

FDIS: Final Draft International Standard. Circulation of approved DIS for final vote.

The following ISO/TC209 documents are at the stages described:

ISO 14644-1	Cleanrooms and Associated Controlled Environments, Part 1: Classification of air cleanliness. FDIS 14644-1 received approval and is proceeding to publication.
ISO 14644-2	Cleanrooms and Associated Controlled Environments, Part 2: Specifications for testing and monitoring to prove continued compliance with ISO 14644-1. This draft is in preparation for issue as FDIS 14644-2.
ISO 14644-1	Cleanrooms and Associated Controlled Environments, Part 3: Metrology and test methods. This draft has been issued as CD 14644-3.
ISO 14644-4	Cleanrooms and Associated Controlled Environments, Part 4: Design, construction and start up. This draft is in preparation for issue as FDIS 14644-4
ISO 14644-5	Cleanrooms and Associated Controlled Environments, Part 5: Operations. WD 14644-5 has been forwarded to ISO/TC 209.
ISO 14644-7	Cleanrooms and Associated Controlled Environments, Part 7: Minienvironments and isolators. WD 14644-7 has been forwarded to ISO/TC 209.
ISO 14698-1	Cleanrooms and Associated Controlled Environments, Biocontamination Control, Part 1: General principles. This draft has been issued as DIS 14698-1.
ISO 14698-2	Cleanrooms and Associated Controlled Environments, Biocontamination Control, Part 2: Evaluation and interpretation of biocontamination data. This draft has been issued as DIS 14698-2.
ISO 14698-3	Cleanrooms and Associated Controlled Environments, Biocontamination Control, Part 3: Methodology for measuring the efficiency of processes of cleaning and (or) disinfection of inert surfaces bearing biocontaminated wet soiling or biofilms. This draft has been issued as DIS 14698-3.
WD xxxx	Working Draft Document for Terms and Definitions

With regard to the issue of drafts by BSI for public comment in the United Kingdom, the present situation is as follows.

European Standards

British Standards

Whilst the current British Standard for cleanrooms mav not be altered while the CEN work is in progress, a need has been recognized to give further guidance on the in situ testing of HEPA filters that is a requirement of BS 5295. For this purpose, BSI published the following document:

The imminent publication of BS EN ISO 14644-1 will result in changes to the status of the Parts of BS 5295. In particular, it should be noted that Parts 1 and 4 of BS 5295 will be withdrawn. Details of other changes will be issued in due course.

Publicly available documents covered in this update report can be obtained from: BSI Standards, 389 Chiswick High Road, London, W4 4AL, Sales Tel: 0181-996 7000, Sales Fax: 0181-996 7001.

Courses

The following courses, to be run at Arizona State University, USA, look interesting:

For more information:

Alliance for Construction Excellence, Arizona State University, PO Box 870204, Tempe, AZ 85287-0204

Fax: (602)965-8172; Phone: (602)965-5324