We had heard Doctors saying “Operation success but patient died”. There are many reasons for this statement, the treatment / surgery might have been late, the age, immune system did not respond, drug not effective etc. This statement might have been more relevant to the failure rate of surgeries due to the operation theatre conditions. One can compare and judge the huge difference between the olden day and the modern-day surgeries. It is incomparable. The first documentation of surgery is dated back to 6th century BC and modern-day operation theatres are phenomenal with technology and the most important advancement would be the clean rooms. AHU [Air Handling Units] plays a major role in the clean room applications. AHU supplies filtered air to the operation tables and has made the surgeries more successful and prevented the microbial invasions into the body during the surgeries. Undoubtedly, AHU has brought a huge difference in reducing the fatality rate after surgery over the years and have saved millions of lives and continued to be! The major factors are the quality of air filtered through 0.3 micron rated filter, the increased air changes per hour, design have brought the viable [Micro-organisms] and non-viable particles in the environment to high degree of control. In a nutshell, it has made a significant contribution in saving millions of human populations as of now.
History of Air handling system [AHU]
Ventilation was provided for the first time in 1855 in the hospital by Brunel.
Sir John Simon in 1864 wrote that ventilation must ‘flow from inlet to outlet’ which can be achieved by mechanical means.
For the first time contamination control was recognized during second world war.
20 Air changes per hour concept was first described by Colebrook in 1946.
Laboratory test has demonstrated that 60 air changes or more gives ‘sudden disappearance of bacterial cloud’.
Downward displacement with minimum turbulence was further investigated by Blowers & Crew in 1960.
The concept of unidirectional or laminar flow was realized in 1961 by Sandia Laboratories.
The first Federal Standard was published in 1963 as FED 209. Different versions were published upto FED 209 D.
In 1992, a metric version [FED 290 E] standard was published.
Cleanroom according to FED 209 E is defined as ‘A room in which the concentration of airborne particles is controlled and which contains one or more clean zones.
Requirement for Clean Rooms
Presence of inanimate particles which may prevent product functioning and reduce life.
Microbe carrying particles whose presence may lead to risk of patient’s life.
Applications of Clean room in Industries
- Electronics: Computers, TV tubes, Flat Screens, Magnetic tape production [Class 1]
- Semiconductors: Integrated circuits for computer memory [Class 10]
- Micro mechanics: Miniature bearings, CD players [Class 10]
- Biotechnology: Antibiotic production and genetic engineering [Class 100]
- Pharmaceuticals: Sterile Pharmaceuticals [Class 100]
- Medical Devices: Heart Valves, cardiac by-pass system [Class 100]
- Hospital: Immunodeficiency therapy, operating rooms, isolation of contagious patients [Class 100]
- Optics: Lenses, Photographic films, Laser requirement [Class 1000]
Clean room Standards
- Federal Standard FED 209E
- British Standard: BS 5295
- German Standard: VDI 2083
- Japanese Standard: JIS B 9920
- Australian Standard: AS 1386
- French Standard: AFNOR X 44101
- Dutch Standard: VCCN-RL-1
- Russian Standard: GOST R 50766-95
- New International Standard: ISO 14644
What is AHU?
AHU stands for Air Handling Units. The air handling unit is an assembly of air conditioning components like fans, cooling coils, filters, humidifiers and dampers which are integrated and installed as a single unit connected to a system of metal ductwork that distributes the conditioned air. An air handling unit is used to circulate and re-condition air as part of a heating, ventilating, and air-conditioning system [HVAC]. The function of AHU is to take outside air, re-condition it and supply it as fresh air to a clean room. The AHU is used to control the following parameters- Air quality, temperature, humidity, air movement, circulation, air changes.
Components of AHU
1.Supply fan-to circulate the conditioned air to various zones.
2.Fan motor – electric motor provides the rotating motion to the supply fan.
3.Cooling coil – provide cooling and dehumidification of air.
4.Filters– used to eliminate contaminated particles of various sizes from the air. Different filters are used according to the application of the AHU system. HEPA filters are used in clean rooms of Pharmaceuticals, Operation theatres.
What is a HEPA filter?
1.HEPA filter -High Efficiency Particulate Air Filter. A dry-type filter in a rigid frame having a minimum particle – collection efficiency of 99.97% for 0.3-micron, monodispersed DOP [Dioctyl phthalate].
2.To meet the HEPA standard, the filter must remove 99.97% or more of all particles which are 0.3 microns in diameter. In other words, for every 10,000 particles that are 0.3 microns in diameter, only three of them pass through. Medical grade HEPA filters are commonly used in pharmaceutical manufacturing and electronic control rooms because they have a greater particulate retention rate. This means medical grade HEPA filters are more efficient in removing harmful viable and non viable particles from the environment.
3.Filters are classified based on EN 1822:2009 standards. HEPA H13-H14 are within the highest tier of HEPA and are considered medical grade quality. Whereas H10-H12 filters only trap 85-99.5% of all particles that are 0.1 microns in diameter, HEPA H13 and H14 trap 99.95% and 99.995% of such particles respectively.
What is Cleanroom?
1.Room in which concentration of airborne particles is controlled and is designed to minimize the introduction, generation and retention of particles.
2.Other relevant parameters e.g., temperature, humidity, and pressure are controlled as necessary.
Types of Clean areas
- Conventional: Turbulently ventilated or non-unidirectional flow.
- Unidirectional flow: known as Laminar Air Flow.
- Mixed flow: Conventionally ventilated but where the product, container-closure and product contact surface are exposed, a unidirectional supply is provided.
- Isolators or microenvironment: Highest level of protection against contamination.
Occupancy States
1.As-Built: Conditions where the installation is complete with all services connected and functioning but no production equipment, materials, or personnel present.
2.At-Rest: Installation complete, equipment installed and operating, but no personnel present.
3.In Operation: Installation complete, equipment installed and operating, with specified number of personnel.
Qualification/Certification of Cleanroom
1.Classification of air cleanliness by particle concentration as per ISO-14644
A discrete-particle-counting instrument shall be used to determine the concentration of airborne particles equal to and greater than the specified sizes at designated sampling locations. The particle counter shall have a valid calibration certificate, the frequency and method of calibration should be as specified in ISO 21501-4. Derive the minimum number of sampling locations, NL, from Table given below.
–Sampling locations
When the area of the cleanroom or clean zone is greater than 1 000 m2, apply the formula to determine the minimum number of sampling locations required. Where NL is the minimum number of sampling locations to be evaluated, rounded up to the next whole number; A is the area of the cleanroom in m2.
–Sampling volume
At each sampling location, sample a volume of air sufficient to detect a minimum of 20 particles if the particle concentration for the largest selected particle size were at the class limit for the designated ISO Class. The single sample volume, Vs, per sampling location is determined by using Formula. Where Vs is the minimum single sample volume per location, expressed in litres; Cn, m is the class limit [Number of particles per cubic metre] for the largest considered particle size specified for the relevant class; 20 is the number of particles that could be counted if the particle concentration were at the class limit.
The volume sampled at each location shall be at least 2 l, with a minimum sampling time of 1 min for each sample at each location. Each single sample volume at each sampling location shall be the same.
Set up the particle counter in accordance with the manufacturer’s instructions including performing a zero-count check. Position the particle counter probe in the plane of the work activity.
The sampling probe shall be positioned pointing into the airflow. If the direction of the airflow being sampled is not controlled or predictable [e.g., non-unidirectional airflow], the inlet of the sampling probe shall be directed vertically upward. The cleanroom or clean zone is deemed to have met the specified air cleanliness classification requirements if the measured values at each of the sampling locations does not exceed the concentration limits determined from table below.
Example
–Periodic classification of air cleanliness by particle concentration
Periodic classification testing shall be undertaken annually in accordance with ISO 14644-1. This frequency can be extended based on risk assessment, the extent of the monitoring system and data that are consistently in compliance with acceptance limits or levels defined in the monitoring plan.
ISO 14644-2 emphasizes the need to consider a monitoring strategy in addition to the initial or periodic execution of the classification of a cleanroom or clean zone in accordance with ISO 14644-1:2015. The monitoring activity provides a continuing flow of data over time, thereby providing a more detailed view of the performance of the installation.
A monitoring plan shall take into account the level of air cleanliness required, critical locations and performance attributes of the cleanroom or clean zone that affect the performance of the installation based on a risk assessment.
2. Air pressure difference test
The purpose of the air pressure difference test is to verify the capability of the cleanroom air movement system to maintain the specified pressure differential between the cleanroom and its surroundings. The air pressure difference test should be performed after the cleanroom has met the acceptance criteria for airflow velocity or air volume flow rate, uniformity of velocity and other applicable tests. This test is applicable in each of the three designated occupancy states, and can also be repeated on a regular basis as part of a routine facility monitoring.
It is recommended that the following items are confirmed before starting the measurement of differential pressure between rooms or between rooms and outside areas:
— values and acceptable range of differential pressure between rooms should be defined;
— supply air volume and balancing of the air handling unit supplies are within specifications;
— cleanroom components that could impact the differential pressure between rooms such as doors, windows, pass through, etc. should be closed. Permanent openings should be kept open during the test;
— the air handling system has been operated and the conditions have been stabilized;
— extraction systems should be operating as agreed and specified.
The pressure differences between each individual cleanroom, clean zone and the connected adjacent room(s) should be measured.
This will include measurement of the pressure difference between classified room(s) connected to the non-classified surrounding environment.
To avoid possible erroneous readings, the following should be considered:
a) Installation of permanent measuring points.
b) Measurements in the cleanroom and clean zone should not be taken near supply air inlets, return air outlets, air movement devices, doors and other localized high air velocity areas that may influence the local pressure at the measuring point.
c) When the measured differential pressure is lower than an agreed value, direction of flow between rooms should be confirmed by flow visualization methods.
The pressure differential may be monitored by periodic observation or by automated instrumentation
Acceptance criteria as per Sep 2004 USFDA guidance.
A positive pressure differential of at least 10-15 Pascals should be maintained between adjacent rooms of differing classification [with doors closed]. In any facility designed with an unclassified room adjacent to the aseptic processing room, a substantial overpressure [e.g., at least 12.5 Pa] from the aseptic processing room should be maintained at all times to prevent contamination.
Acceptance criteria as per EU Annex-1 2020 guidance.
Adjacent rooms of different grades should have pressure differentials of a minimum of 10 pascals [Guidance value].
3.Airflow test
This test is performed to measure the supply airflow introduced into both unidirectional and nonunidirectional cleanrooms or clean zones.
In unidirectional applications, the supply airflow velocity can be measured with individual point readings to allow for the measurement of velocity and determination of uniformity of velocity. The average of the individual velocity point readings may be used to calculate the supply airflow volume and air change rate [Air changes per hour].
In non-unidirectional applications, individual velocity point readings are typically not required as uniformity of velocity is generally not necessary. In these cases, airflow volume readings may be measured directly and then used in calculating the air change rate [Air changes per hour] for the cleanroom or clean zone.
Acceptance criteria as per Sep 2004 USFDA guidance
A velocity of 0.45 meters/second [90 feet per minute] has generally been established, with a range of plus or minus 20 percent around the setpoint. Higher velocities may be appropriate in operations generating high levels of particulates.
Acceptance criteria as per EU Annex-1 2020 guidance.
Unidirectional airflow systems should provide a homogeneous air speed in a range of 0.36 – 0.54 m/s [Guidance value] at the working position.
The purpose of this test is to demonstrate that the airflow direction and its uniformity of velocity conform to the design and performance specifications. The airflow direction test can be conducted in the at-rest state to determine the basic cleanroom airflow patterns and can be repeated in the operational state simulating actual operations.
The purpose of these tests is to measure airflow velocity and uniformity, and supply air volume flow rate in cleanrooms and clean zones. Measurement of velocity distribution is necessary in unidirectional airflow cleanrooms and clean zones, and supply air volume flow rate in non-unidirectional cleanrooms. Measurement of supply air volume flow rate is carried out to ascertain the air volume supplied to the cleanroom or clean zone per unit of time. The supply air volume flow rate is measured either downstream of final filters or in air supply ducts; both methods rely upon measurement of velocity of air passing through a known area, the air volume flow rate being the product of velocity and area.
When measuring airflow velocity, the following conditions should be considered carefully:
a) Probe direction should be chosen appropriately under the consideration on the airflow velocity;
b) Measurement should be conducted during sufficient time for repeatable readings and the average velocity or air volume flow rate should be recorded.
The airflow velocity should be measured at approximately 150 mm to 300 mm from the filter face or entry plane.
The minimum number of measuring points should be determined by the formula, where N is the minimum number of measuring points and A is the measured area in m2.
Where the average velocity is required for a zone with unidirectional airflow, the average velocity is calculated from the formula:
Va = (ΣVn) / N where Va is the average velocity in m/s; ΣVn is the sum of all the measured velocities (Vn) in m/s; Vn is the measured velocity at each of the grid cell centres in m/s; N is the number of locations at which the velocities (Vn) were measured.
Air changes per hour [ACPH] acceptance criteria according to guidance
4.Airflow direction test and visualization
The purpose of airflow direction test and visualization is to demonstrate that the airflow direction and its uniformity of velocity conform to the design and performance specifications.
The airflow direction test and visualization can be performed by the following four methods:
a) Tracer thread method- The test is carried out by observation of tufts, e.g., silk threads, single nylon fibres or thin film tapes. These are set on the tip of support sticks or mounted on the crossing points of thin wire grids in the airflow. They provide visual indication of the airflow direction and fluctuations due to turbulence. Effective lighting will aid observation and recording of the indicated airflow.
b) Tracer injection method- The test is carried out by observation or imaging of the behavior of tracer particles, which can be illuminated by high-intensity light sources. The test provides information about the airflow direction and uniformity of velocity in a cleanroom, clean zone or controlled zone. The tracer particles can be generated from materials such as de-ionized [DI] water, sprayed or chemically generated alcohol/glycol, etc. The source should be carefully selected to avoid contamination of surfaces. The desired size of droplets should be considered when selecting the droplet generation method. Droplets should be large enough to be detected with the available image processing techniques, but not so large that gravitational or other effects result in their motion diverging from that of the airflow being observed.
c) Airflow visualization method by image processing techniques- The processing technique requires a digital computer with suitable interfaces and the appropriate software. For greater spatial resolution, devices such as a laser light sources can be used.
d) Airflow visualization method by the measurement of velocity distribution- The velocity distributions of airflow can be determined by setting air velocity measuring apparatus, such as thermal or ultrasonic anemometers, at several defined points in the cleanroom or clean zone under investigation. Processing of the measured data provides the information about the airflow distribution.
By methods a) and b), airflow in the cleanroom or clean zone is actually visualized by the use of fibre tracer thread, or tracer particles. Devices, such as video cameras, record the profiles. The fibre tracer thread or tracer particles should not be a source of contamination and should follow the airflow profile accurately. Other apparatus such as a tracer particle generator, and high intensity light source may be used for these methods.
Method c) is used to demonstrate quantitatively the airflow velocity distributions in the cleanroom or clean zone. The technique is based on tracer particle image processing techniques using computers.
Care should be taken to ensure that the personnel undertaking the test do not interfere with the airflow patterns being investigated.
5.Recovery test
1.The recovery test is performed to determine whether the cleanroom or clean zone is capable of returning to a specified cleanliness level within a finite time, after being exposed briefly to a source of airborne particulate challenge. This test is not recommended for unidirectional airflow. When an artificial aerosol is used, the risk of residue contamination of the cleanroom or clean zone should be considered.
2.This test is performed to determine the ability of the installation to reduce the concentration of airborne particles by dilution. This test is only recommended for non-unidirectional airflow systems as the recovery performance is based on the dilution and mixing of the air found in non-unidirectional airflow systems, and not unidirectional airflow systems, where contamination is removed by the unidirectional flow of air. The recovery performance of a non-unidirectional cleanroom is affected by air distribution characteristics such as ventilation effectiveness, thermal conditions, and obstructions. The recovery test can be performed using an aerosol photometer. When an artificial aerosol is used, the risk of residue contamination of the cleanroom or clean zone should be considered.
3.Recovery performance is evaluated by using the 100:1 or 10:1 recovery time and/or the cleanliness recovery rate. The 100:1 or 10:1 recovery time is defined as the time required for decreasing the initial concentration by a factor of 100 times (or 10 times). The cleanliness recovery rate is defined as the rate of change of particle concentration by time. It is possible to estimate both of these from the same particle concentration decreasing curve.
4.The purpose of the recovery time test is to evaluate an actual time interval for the concentration to reach target cleanliness level after the particle concentration in the cleanroom or clean zone has temporarily become higher due to planned maintenance shutdown, or unplanned plant failure. The purpose of evaluation by recovery rate is to establish the local ability to recover the cleanliness after the particle concentration around the measuring point has temporarily become higher. The 100:1 test is not recommended for ISO Classes 8 and 9. The particle size used in this test should be less than 1 μm. The cleanroom area to be examined should be contaminated with an aerosol while the air-handling units are in operation. Raise the initial particle concentration to more than 10 or 100 times depending on the target cleanliness level. Commence measurements at not more than 1 min intervals and record time and concentration.
6.Temperature test
The purpose of this test is to verify the air temperature levels are within the control limits over the time period for the area being tested. Target level of temperature for Pharmaceutical Industry: 20 Deg.C. 18-22 Deg.C is maintained as range.
7.Humidity test
The purpose of this test is to verify moisture [Expressed as relative humidity] levels are within the control limits over the time period for the area being tested.
Acceptance criteria as per ISO-14644-4
The typical relative humidity set range is between <65% to >30%. Outside this range, suitable measures should be considered to meet process and personnel requirements.
However low RH is required for moisture sensitive materials [e.g., 25+/-5%]
8.Installed filter system leakage tests
These tests are performed to confirm that the final high efficiency air filter system is properly installed by verifying the absence of bypass leakage in the air filter installation and that the filters are free of defects [Small holes and other damage in the filter medium, frame, seal and leaks in the filter bank framework]. These tests are not used to determine the efficiency of the filter medium. The tests are performed by introducing an aerosol challenge upstream of the filters and scanning downstream of the filters and support frame or sampling in a downstream duct.
Scan with an aerosol photometer and the probe traverse scan rate should be approximately 5 cm/s. While scanning, any indication of a leak equal or greater than the limit which characterizes a designated leak should be cause for holding the probe at the leak location. The location of the leak should be identified by the position of the probe that sustains the maximum reading on the aerosol photometer.
Acceptance criteria as per ISO-14644-3, A leak detected in excess of 0.01% of the upstream mass concentration is deemed to exceed the maximum allowable penetration. However, for filter systems of an integral efficiency at MPPS ≥ 99.95 % and less than 99.995 %, the acceptance criterion is 0.1 %.
Acceptance criteria as per Sep 2004 USFDA guidance, A single probe reading equivalent to 0.01 percent of the upstream challenge would be considered as indicative of a significant leak and calls for replacement of the HEPA filter or, when appropriate, repair in a limited area. A subsequent confirmatory retest should be performed in the area of any repair.
Upstream aerosol challenge
The mass median particle diameter for this production method is typically between 0.3 μm to 0.7 μm with a geometric standard deviation of up to 1.7
The concentration of the aerosol challenge upstream of the filter should be between 1 mg/m3 and 100 mg/m3.
Measure the aerosol concentration upstream of the filters. This aerosol concentration should be used as the upstream 100% reference for the photometer. Downstream measurements are then displayed as percentage penetration of upstream concentration. The probe should then be traversed at a scan rate not exceeding 5 cm/s using overlapping strokes [1 cm recommended]. The probe should be held in a distance of 3 cm or less from the downstream filter face or the frame structure. Scanning should be performed over the entire downstream face of each filter, the perimeter of each filter, the seal between the filter frame and the grid structure, including its joints. Measurements of the aerosol upstream of the filters should be repeated at reasonable time intervals between and after scanning for leaks, to confirm the stability of the challenge aerosol concentration.
9.Containment leak test
This test is performed to determine if there is intrusion of unfiltered air into the cleanroom or clean zone(s) from outside the cleanroom or clean zone enclosure(s) through joints, seams, doorways and pressurized ceilings.
10.Electrostatic and ion generator tests
The purpose of these tests is to evaluate electrostatic voltage levels on objects, static-dissipative properties of materials and the performance of ion generators [i.e., ionizers] used for electrostatic control in cleanrooms or clean zones. Electrostatic testing is performed to evaluate the electrostatic voltage level on work and product surfaces and the static dissipative properties of floors, workbench tops, etc. The ion generator test is performed to evaluate the ionizer performance in eliminating static charges on surfaces.
11.Particle deposition test
The purpose of this test is to verify the quantity and size of particles deposited from the air in the cleanroom onto a surface over an agreed period of time.
12.Segregation test
The purpose of this test is to assess the separation effectiveness achieved by a specific airflow, challenging the lesser classified area with particles and determining the particle concentration in the protected area at the other side of the segregation.
Guidance requirement for requalification frequency/routine monitoring for clean room parameters
13.Optional environmental tests
- Lighting level and uniformity test [400-750 lux for visual tasks]
- Noise level test [55-65 decibel]
Ultimate Objective: Assurance of product quality for patient safety.
Note-The images given for representation in this blog are taken from Google Images. Many thanks for Google.