Cleanrooms, laboratory areas, isolators and biosafety workspaces (microbiological safety cabinets) require a level of cleanliness and microbial control (achieved through disinfection) according to the intended use of the area. With cleanrooms this relates to microbial levels according to the class or grade of the room; with containment laboratories and biosafety cabinets this is with the intention of eliminating specific pathogens.
Decontamination can be undertaken using more traditional (and manually intensive) methods, such as spraying and wiping a suitable disinfectant onto a surface. Disadvantages with the manual approach include the need to remove residuals and the difficulty in ensuring coverage over an area (particularly in rooms). There are also concerns with the evaluation of the technique, which requires an extensive field trial to be conducted.
As an alternative, such areas can be effectively ‘biodecontaminated’ using gassing systems (‘bio’ denoting the elimination of microorganisms as opposed to chemical detoxification). There is considerable literature relating to the decontamination of isolators using gassing systems and the aim is not to repeat this here; instead the focus of the paper is with the decontamination by the use of gas of cleanrooms, containment laboratories and biosafety cabinets (1). Less has been written about the decontamination of these areas and the use of gassing systems to decontaminate these rooms and devices is increasing (or alternative chemical agents are being marketed). An alternative term to decontamination is fumigation, although this has closer connections with the use of formaldehyde and other poisonous fumigants and so ‘decontamination’ is the preferred term for this paper.
For cabinets, established approaches involve ‘gassing’ (a term which may refer to the use of a gas or to a vapor; the word vapor refers to a substance that in its natural state is a solid or liquid at room temperature, such as steam; whereas a gas in its natural state at room temperature would still be a gas, such a nitrogen) (2). Such methods have been used for the decontamination of microbiological safety (‘biosafety’) cabinets for decades, albeit more often using formaldehyde. The application of gassing systems to rooms (or suites of rooms) is a more recent development. Here hydrogen peroxide vapor is being used more frequently for decontamination. This includes hospital wards, containment laboratories and pharmaceutical facility cleanrooms (3).
Gaseous ‘sterilants’ are effective surface decontaminating agents in that they will treat the outside of a device (or the primary packaging in which the device is held). The process is not typically referred to as ‘sterilization’ because unlike accepted forms of sterilization, like radiation or heat, the agent does not penetrate into the item being treated (4). Thus the terms ‘decontamination’ (or ‘bio-decontamination’) or sanitization are preferred. The key parameters affecting the effectivity of gas treatment are the active concentration, temperature, duration of exposure, and relative humidity (5).
In the past the primary method of decontaminating an area was through gas fumigation, using a substance like formaldehyde (formaldehyde is a gas which is soluble in water). This was despite few evaluation studies being conducted on the biocidal effectiveness of formaldehyde in the gaseous state, especially in consideration of the optimal parameters for microcidal kill (in terms of temperature and humidity). In addition, there are health and safety concerns associated with the use of formaldehyde, attributable to its toxicity and classification as a carcinogen. Alternative methods for gas decontamination of rooms are typically based on agents like hydrogen peroxide, chlorine dioxide and ozone.
The trends with the use gas or vapor to decontaminate an area are, firstly, the extension of the process from containment laboratories to cleanrooms; and, secondly, a reduction in the use of formaldehyde and a greater take-up of hydrogen peroxide or alternative agents. This paper assesses the current technologies and process steps required for the effective biodecontamination of cleanrooms and containment laboratories.
As indicated in the introduction, formaldehyde is an established fumigant and one traditionally associated with containment laboratories and biosafety cabinets. While it is unlikely that a cleanroom manager today would opt for formaldehyde fumigation, the use of the agent remains relatively widespread worldwide and this section focuses on the use of the chemical together with its advantages and disadvantages.
Formaldehyde is a naturally-occurring organic compound with the formula CH2O. It is the simplest of the aldehydes. Formaldehyde is produced industrially by the catalytic oxidation of methanol. The production of formaldehyde was accidentally discovered by Alexander Mikhailovich Butlerov in 1859, with the official discovery being made in 1868 by A. W. Hofmann. From the late nineteenth century formaldehyde has become a major industrial product. One application is decontamination and formaldehyde vapor was the most common choice for decontaminating safety cabinets, and some rooms, at least until the 1990s. Formaldehyde remains in use, although many users have transitioned to systems that use hydrogen peroxide.
Formaldehyde vapor is theoretically effective biocidal agent (the degree to which it has been empirically tested is touched on below). To assess the effectiveness of formaldehyde biological indicators can be used, placed in appropriate locations. The chemical acts as an alkylating agent, inactivating microorganisms by reacting with carboxyl, amino, hydroxyl and sulphydral groups of proteins as well as the amino groups of nucleic acid bases. For formaldehyde to act to maximum efficacy it needs to reach the microbial cell. To do so formaldehyde must be able to dissolve at adequate concentrations in a film of moisture in the immediate vicinity of the microorganisms (6). Without such conditions, formaldehyde penetrates poorly.
To optimize the use of formaldehyde, the chemical is used in conditions, created by a proprietary fumigation device, which are both humid and warm (that is above 65% relative humidity and above 200°C). Alternatively, paraformaldehyde (the polymerization product of formaldehyde) can be vaporized in a pan on an electric element on the basis of 12 g per m3 with simultaneous evaporation of 4 liters of water to supply the necessary humidity.
The main concern with the use of formaldehyde relates to the chemical having irritant and toxic properties. Use of the chemical carries a risk of respiratory damage and skin sensitization reactions. Formaldehyde can also react with chlorine to form bis- (chlormethyl) ether, which is a potent lung carcinogen. To safeguard against this, chlorine-containing disinfectants must be removed from areas prior to fumigation. An additional risk arises from formaldehyde being an explosion risk at a concentration of 7.75% (or higher) in dry air. This risk does not present itself at lower concentrations or in humid air.
These risks noted, formaldehyde remains in common use, especially in the laboratory setting where it is used for the decontamination of cabinets and rooms. These two applications are considered below.
Formaldehyde: decontamination of cabinets
Where formaldehyde is used for the decontamination of biosafety cabinets and equivalent devices the objective is to destroy any microorganisms that may have penetrated the High Efficiency Particulate Air (HEPA) filter. This is achieved through exposing of the downstream side of the HEPA filter and the ductwork to formaldehyde.
A generalized procedure to achieve this involves the following steps (alternatively some cabinets have automatic fumigation cycles programmed into the controls and in these circumstances the manufacturers' instructions should be adhered to):
- Switch off the cabinet fans and wait at least 30 seconds.
- If the cabinet is a recirculation type, fit the fumigation adaptor kit to the discharge and position the other end to vent to atmosphere. A recirculation type of cabinet is ideal. Passive migration of the fumigant through the filter can occur but this does not lead to an optimal performance.
- Close the manual shut-off damper.
- Fill the vaporizer with the correct amount of formalin and screw on the aluminum cap - finger tight, having checked the gasket in the cap is undamaged. Place the vaporizer inside the cabinet.
- Fit the closure panel (or night door) and fully seal the front screen and closure panel with sealing tape to ensure there are no leaks.
- For safety reasons, place a notice on the front of the cabinet indicating fumigation is in progress.
- Switch the vaporizer on.
- After approximately 10 minutes (when half of the formalin will have been used) switch the cabinet fans on for 10 - 15 seconds.
- After a further 20 - 30 minutes switch the cabinet fans on again for 10 - 15 seconds.
- Leave the cabinet in this condition preferably overnight, but for a minimum of 6 hours (or preferably overnight).
- If the cabinet is a recirculation type check the exhaust of the fumigation adaptor kit is in a position to discharge safely and open the manual shut-off damper.
- Before venting the formaldehyde check that no people are in the vicinity of the exhaust outlet and that gas will not enter any open windows nearby.
- Exhaust the formaldehyde from the cabinet by switching on the fans and opening the closure panel/night door slightly (remove bung if fitted or crack open) until the majority of the formaldehyde has been exhausted. After about 10 minutes the night door may be removed completely.
- Any poly-formaldehyde residue in the vaporizer may be removed be heating with water containing a little mild detergent.
- Run the cabinet for at least a further 15-20 minutes to remove the last traces of formaldehyde.
- If the cabinet is a recirculation type the fumigation adaptor kit must be removed before the cabinet is used again.
It is especially important that following decontamination, the cabinet must be purged (aerated) of all residual formaldehyde.
Formaldehyde: decontamination of rooms
A similar controlled process is undertaken for the decontamination of cleanrooms and laboratory spaces. This should only be attempted if there is a means of exhausting the formaldehyde vapor from the room, via an extract system controlled from the outside of the room. The extract should be a total loss system with no possibility of formaldehyde being ducted to other areas. Before commencing fumigation the indoor space must be completely sealed to prevent escape of formaldehyde vapor into other areas.
Calculations need to be undertaken to estimate how long it will take to purge all the formaldehyde from the room after fumigation is complete. Such calculations should be based on room volume and the rate of air extraction through the particular exhaust system that will be used (7). The calculation needs to assess the initial formaldehyde concentration in the room and the target, which is the reduction of formaldehyde well below 2 parts per million (ppm) or 2.5 mg.m-3. For this assessment the following formula is suitable:
Time (minutes) x 25 = room volume (m3) / extraction rate (m3.min-1)
For the decontamination run it is typical to use 100 mL formalin plus 900 ml water per 28.3 m3 (1000 ft3) of room space.
As with the application of formaldehyde for the decontamination of cabinets, a series of steps can be followed for room decontamination:
- Switch off all forced air ventilation systems, extract systems and any fume cupboards and microbiological safety cabinets in the room. Additionally, deactivate fire alarm system smoke detectors.
- Seal up any external ventilation grilles.
- Confirm that the point from which the formaldehyde will be exhausted is free from obstruction.
- Place the appropriate quantities of formalin and water mixture into the heater unit. Activate the heater and leave the room immediately.
- Lock the door and effectively seal around the edges with tape.
- After a period of not less than 12 hours (for this reason, the procedure is best carried out overnight), the room must be well ventilated. Purge the space by using the remote switch to activate the extraction system (open air handling system dampers if necessary).
- Allow the room to purge for at least the time calculated as necessary to remove the formaldehyde.
- Check levels of residual formaldehyde in the room with suitable air monitoring equipment (such as a ‘formaldemeter’ or air sampling tubes).
- Responsible personnel should only enter the room if the level of formaldehyde is below 2ppm. It is recommended that personal protective equipment be worn.
- Check the room and all surfaces for formaldehyde residues and clean up as necessary.
- Remove all sealing materials.
- Other personnel can enter the room once formaldehyde levels are below 0.5 ppm.
Although formaldehyde remains in use in the laboratory setting, it is losing ground to hydrogen peroxide vapor. This is particular so with rooms that cannot be pre-cleaned prior to decontamination (such as areas that handle biohazards). Moreover, hydrogen peroxide vapor is the process of choice where the gaseous decontamination of cleanrooms within a GMP setting is required.
Hydrogen peroxide vapor
Hydrogen peroxide is clear, colorless, ‘water-like’ in appearance, and it has a characteristic pungent odor. Hydrogen peroxide vapor has a rapid antimicrobial efficacy, good material compatibility and, in comparison with formaldehyde, lower safety concerns. With microcidal efficacy, hydrogen peroxide is active against a wide range of organisms and this broad spectrum of activity is a product of the oxidizing capacity of the chemical. The chemical causes damage to cellular proteins, lipids and nucleic acids. With efficacy, hydrogen peroxide is more efficient in the gaseous form than in liquid phase.
The efficacy of hydrogen peroxide can be affected by the presence of both organic (such as proteins and lipids) and inorganic materials, which may reduce the penetration and activity of the agent. This is certainly the case in the presence of bacterial spores and Mycobacterium species (8), which are more resistant than other vegetative bacteria due to their unique lipophilic cell wall structure. The additional presence of organic materials can act as an additional shield to protect such microorganisms further. In addition there is some evidence to suggest that in, certain circumstances, microorganisms that produce catalase (a hydrogen peroxide degrading enzyme), such as species of Streptococcus (containing pyruvate oxidase), may be more resistant to the hydrogen peroxide treatment (9). Where these organisms are of concern (as might be evidence through environmental monitoring) this should be considered in a risk assessment.
An operational advantage with hydrogen peroxide is that it is compatible with a variety of different materials, such as plastics, metals, paintwork and electrical equipment. With safety although there are operational risks from the vapor, the risks are lower at the end of the process compared with formaldehyde for hydrogen peroxide is thermodynamically unstable and it decomposes to form water and oxygen.
Safety concerns when using hydrogen peroxide include the vapor being an irritant of the eyes, mucous membranes and skin and it may cause lung irritation if inhaled. Additionally, skin contact with liquid hydrogen peroxide can cause temporary bleaching of the skin or redness and blisters if it is not immediately washed away.
There are two methods use to apply hydrogen peroxide for room or cabinet decontamination. These are:
- Aerosols. Here a commercial system produces a fine mist (particle sizes between 8 and 10 microns) of 5% hydrogen peroxide in air, with <50 ppm Silver ions, <50 ppm phosphoric acid, <1 ppm Arabica gum as catalysts. Over time, the aerosols collapse, the hydrogen peroxide reacts, and then degrades to safe conditions. There is little published validation of this method in hospital situations.
- Non-condensing vapor. With this approach, vapor is produced by a four-step sequence: an enclosed volume is first dehumidified. Then hydrogen peroxide (typically at a concentration of 35%) is vaporized under controlled conditions of temperature, humidity, and pressure so that there is no condensation. This state is maintained in the enclosure for a prolonged period during which super lethal concentrations of hydrogen peroxide are maintained in air for disinfection (10). In terms of microbial kill, this is the most important stage. Finally, the enclosure is purged with air (catalytic aeration) so that the concentration of hydrogen peroxide is below the product exposure limit (as an indicator of safety) (11).
Of these two approaches the second one is the more common. Non-condensing vaporised hydrogen peroxide is either referred to as VHP (which is trademarked) or as hydrogen peroxide vapor (HPV) in literature. For this reason HPV is used in the remainder of this paper to denote hydrogen peroxide vapor.
In addition to the different forms of generation, hydrogen peroxide vapor systems are often classified as “wet” or “dry” process. With this differentiation, hydrogen peroxide vapor can be introduced into a given area up to a certain concentration, dependent on the isolator temperature and humidity, to a saturation level or dew point. If the concentration of hydrogen peroxide increases above this level it will condense onto the surfaces of the isolator (forming condensation or micro-condensation). In the case where micro-condensation is formed and maintained during the cycle, this is considered a “wet” process. If the vapor concentration is maintained below the dew point during the cycle this often referred to a “dry” process (although the vapor itself will not be completely “dry”) (12). Although this description is useful in distinguishing between the two different processes, the term “wet” refers only to the fact that micro-condensation has occurred and this may not be visible to the naked eye. Different proprietary hydrogen peroxide generation systems claim to work on either “dry” or “wet” processes. Both, as far as this distinction matters, appear to be effective.
HPV is commonly used to decontaminate isolators. When used with barrier systems and rooms, HPV is a relatively rapid decontamination technology. Because the process, as discussed earlier, is a decontamination one, where critical surfaces are required (as would be the case with aseptic processing), these need to be separately sterilized.
Hydrogen peroxide process
A series of steps are required for decontamination using hydrogen peroxide. With this, vapor is produced through the use of a generator. Generators operate in a similar way, forming a closed loop with the area to be fumigated. Air is circulated through the generator in a four stage fumigation process (13). This process is:
With dehumidification, the humidity levels are reduced to a level below 40%. Some manufacturers of ‘dry’ HPV systems state that the dehumidification step is not required.
For the conditioning stage, hydrogen peroxide gas (generated by vaporization of a 35% liquid hydrogen peroxide) is introduced to raise the concentration to a predetermined level. Sometimes this is called the 'gassing' phase.
The decontamination phase is where the hydrogen peroxide concentration is maintained at a concentration below the condensation point, generally at 0.1-1.5mg/L at 25°C. Sometimes this step is referred to as the 'dwell' phase.
With aeration, the area is aerated to reduce peroxide concentrations to below 1 part per million. This is for occupational safety reasons. The longest phase in the cycle
While designing the control system for HPV cycle, for cleanrooms and isolators, the following factors should be considered (14):
- The cycle should be designed in such a way that allows the complete airflow path to be subjected to decontamination, including the HEPA filters, valves, ducts and so forth.
- The material properties of the load contents should be checked to ensure compatibility with the HPV.
- With isolators, the room surrounding the isolator should be temperature controlled. Fluctuations in room temperature will cause fluctuations in the temperature of the isolator’s exterior surface, leading to condensation on the isolator’s interior surfaces.
- The surface area of the load and the material is more important than the volume and contents of the load (this is essential for cycle development, as discussed below). Functionality must be designed in such a way that all moving parts inside the isolator are exposed to the gas. An intermittent movement of moving parts can be planned during a phase of cycle, if necessary. A glove-holding device and half-suit hangers should be used to keep gloves and half-suits from contacting any surfaces during decontamination.
- The aeration cycle must be designed in such a way that residual concentration from the wrapped goods reduced to a safe level.
- Provisions for holding the gloves in a position which means that the inner portion of the gloves and sleeves are exposed to the gas during the cycle.
- The opening and closing of the tunnel gate should be automated as required during or after the cycle.
- Chemical and biological indicators are required during validation and for annual re-qualification.
To demonstrate effectiveness a suitable HPV cycle should be developed and undergo validation. The effectiveness is demonstrated with the use of chemical indicators, to show vapor distribution, and biological indicators. For biological indicator selection,
Geobacillus stearothermophilus spores are the most resistant to HPV (15). For the biological indicators a population of >106 is typical, with a resistance to hydrogen peroxide expressed as a D-value of between 1 and 2 minutes. With the configuration of the biological indicator, the spores are usually located on a stainless steel concave disc, which is sealed inside a Tyvex pouch. The qualification should assess the influence of different construction material surfaces on inactivation of spores. Generally, plastic/elastomeric materials have generally higher resistance (D-values) compared with stainless steel and glass.
As with any sterilization or decontamination process, it is possible for failure to occur. To guard against this, cycles are designed for overkill. It is also possible for false positive results to be obtained. This can arise, for instance, if part of the pouch is not exposed correctly as with placing the biological indicator flat against a wall (16).
Comparing formaldehyde and hydrogen peroxide efficacy
The choice faced by users is between formaldehyde and hydrogen peroxide. In GMP processing, the choice is almost always towards hydrogen peroxide vapor. In laboratories, especially those used for containment, and with biosafety cabinets the selection is more even. Certainly older systems tend to use formaldehyde.
With formaldehyde, the effectiveness of the agent is based on historic assumption and there are few documented cases regarding its effectiveness. Certainly it is not easy to find data from confirmatory tests or comparison with HPV in this regard. The effectiveness of formaldehyde is considerably reduced if used at suboptimal ambient temperature or humidity. Moreover, temperature and relative humidity are rarely controlled during routine fumigations. HPV, in contrast, has been reported in a number of studies to be active against a wide range of organisms (17). However, as stated earlier, HPV is affected where surfaces have not been properly cleaned, especially where protein is present on surfaces.
Some of the advantages and disadvantages of formaldehyde and hydrogen peroxide are shown in Table 1, below.
Table 1: Comparison of formaldehyde and hydrogen peroxide for decontamination
Long experience of successful use to decontaminate rooms and safety cabinets.
Inexpensive and easy to handle.
Simple to use and easy to detect.
Claimed broad spectrum efficacy.
Effective against M. tuberculosis.
Slow acting, poor penetration.
Removal at end of decontamination
Strictly regulated in some countries.
Health effects include being toxic and carcinogenic
Reacts with chlorine to form bischloromethyl ether.
Broad spectrum, rapid antimicrobial.
Breaks down into non-toxic substances.
Efficacy can be assessed using chemical and biological indicators.
Efficacy affected by presence of organic
and inorganic materials (e.g. proteins and lipids)
Some catalase producing bacteria can show higher resistance.
Requires specialist equipment.
With both formaldehyde and HPV the efficacy is affected by ambient temperature and efficacy reduces at lower temperatures. Factors affecting the efficacy of both agents are:
- Composition of suspending fluid
- Microbial concentration
- Presence of protective agents
In selecting between the two agents, there is a substantially greater risk to safety from the use of formaldehyde compared to that with HPV. In relation to matters of GxP, the effectiveness of HPV can more easily be assessed through the use of chemical and biological indicators.
Alternative gassing agents
Although hydrogen peroxide and formaldehyde remain the predominant agents used for room and cabinet decontamination, there are alternative systems. This closing section of the paper considers some of these.
Ethylene oxide is an alky epoxide agent and it is deployed as a gaseous chemical sterilant. It is relatively stable and able to penetrate most polymeric materials. Biocidal activities are exhibited when the agent is dissolved in water. Here the concentrations required for biocidal effect tend to be quite high, in the order of 400-2,000 mg/L. An advantage is that many of the materials that function as a target for fumigation, such as metal and glass, do not absorb ethylene oxide. Consequently, little or no residue removal is required when using this fumigant. Additionally, the gas is ideal for thermo-labile devices as its application is performed at low temperatures (18).
Workplace exposure limits describe ethylene oxide as capable of causing cancer, therefore precautions are required. Ethylene oxide has a flammability range from 3-100% by volume in air; thus the agent should be supplied with inerting chemicals, designed to contain any explosive event.
Propylene oxide possesses many of the sterilant properties described for ethylene oxide, although a longer processing time is required. The use is generally confined to the food industry. The advantage is with the agent having narrower flammability.
Peracetic acid is an oxidizing agent. It can be used in the liquid form or in the vapor phase. Like hydrogen peroxide, the chemical is sporicidal. In the vapor phase peracetic acid displays an optimal activity at 80% relative humidity (RH). The agent has a slower decay rate in an open chamber than hydrogen peroxide. The decomposition by-products include acetic acid, hydrogen peroxide, water and oxygen. In terms of advantages, peracetic acid is not absorbed as easily as hydrogen peroxide by cellulose-based materials.
Chlorine dioxide is also an oxidizing agent and a sporicide. In the gaseous form it is relatively short-lived and used at 25-30°C and at a concentration of 10-50 mg/L, at 80% relative humidity. Chlorine dioxide has a typical 8 hour run time for a typical application. Applications are limited because the molecule has a damaging effect on some materials (19). The use of chlorine dioxide has been tested out in a number of hospital facilities. One study showed chlorine dioxide to exhibit effective kill of Bacillus anthracis spores, together with spores of Bacillus atrophaeus and vegetative cells of both Francisella tularensis and Yersinia pestis (20). Chlorine dioxide kills microorganisms by disrupting proteins, interfering with protein synthesis and membrane transport.
Ozone is a natural form of activated oxygen and it is formed when oxygen is exposed to a high-energy field. It is a triatomic molecule (O3), consisting of three oxygen atoms. Ozone is much less stable than oxygen (O2), breaking down, with a half-life of about half an hour in the lower atmosphere, into oxygen. Ozone occurs naturally in the atmosphere and it is produced during lightning storms and continuously occurring in the stratosphere due to action of ultraviolet light.
As a sterilant, ozone is classed as an oxidizing agent, and it breaks down into oxygen molecules and oxygen atoms, which have high oxidation potential. Ozone acts on the microbial cell membrane and damages the membrane structure causing metabolism disruption. For secondary action, ozone infiltrates the cell membrane and destroys lipoprotein and lipopolysaccharide, changes permeability and causes cytolysis and cell death. As well as being effective against prokaryotic organisms, ozone is an effective protozoan cysticide (21).
Ozone is used across a variety of industrial settings to sterilize water, as well as a disinfectant for surfaces. However, there is little in the way of case studies to support its use for air disinfection. Effective applications have been reported by use at between 2 and 10% by weight. The case against consideration of ozone for the decontamination of containment areas is the fact it will harm and destroy materials used in containment facilities, especially when used at a high concentration.
The technology for plasma generation and its known inactivation of microorganisms has been known since the 1950s, although commercial applications remain slow to emerge. Plasma is energetically distinguishable from solids, liquids and gases. Plasma can be produced by the action of very high temperatures or electric or magnetic fields, normally composed of clouds of ions, electrons and neutral species. With anti-microbial action, electrical discharge can generate free radicals and other potentially biologically active species from hydrogen peroxide.
Whichever agent is used, the process used must be qualified and appropriate distribution of the agent and microbial kill demonstrated, with respect to the area intended to be treated. Key parameters for an assessment include:
- Area review: size, shape, contents and temperature. Depending on the cabinet or room size, fans may need to be distributed to ensure adequate circulation, or, alternatively, the HVAC system can also be used for efficient vapor delivery and decontamination.
- Distribution studies: the distribution of the vapor can be verified in the room using electrochemical or spectrophotometric sensors, as well as chemical indicators.
- Validation studies: microbiological and chemical indicators may be used to verify antimicrobial efficacy in the area. A suitable endospore forming bacterium should be used. More often these are Geobacillus stearothermophilus spores.
Environmental monitoring represents an important means by which the effectiveness of contamination control measures can be assessed, especially in environments that are required to be controlled or classified. Culture based methods can be used to assess bioburden on surfaces and such data can be trended. Environmental monitoring can be used to help set the frequency of decontamination.
This paper has examined the decontamination of process rooms, containment laboratories and biosafety cabinets using a chemical gas or vapor treatment. The focus has primarily been with formaldehyde and hydrogen peroxide; with some alternative approaches also described. Formaldehyde is one of the oldest gas processes and it is still used in many laboratory settings; its use has declined, however, due to safety concerns. Hydrogen peroxide is a rising technology, already established for the decontamination of isolators; these days the technology is increasingly regarded as a suitable alternative for rooms and cabinets. In discussing these two technologies, the paper has outlined the efficacies of the processes along with some of their advantages and disadvantages. While the different agents have their merits, the recommendation would be to use hydrogen peroxide based technologies.
- Sandle, T. (2013) Sterility testing of Pharmaceutical Products, PDA / DHI, Bethesda, MD, pp129-160
- Sandle, T. (2013) Sterility, Sterilisation and Sterility Assurance for Pharmaceuticals: Technology, Validation and Current Regulations, Woodhead, Cambridge, UK pp111-128
- Doll, M., Morgan, D.J., Anderson, D. and Bearman, G. (2015) Touchless Technologies for Decontamination in the Hospital: a Review of Hydrogen Peroxide and UV Devices, Curr Infect Dis Rep.;17(9):498
- Bruch, C. W. (1961). Gaseous Sterilisation, Annual Review of Microbiology, Vol. 15: 245 -262
- Christensen, E. A., and H. Kristensen (1991). Gaseous sterilisation. In Russell, A.D., Hugo, W.B. and Ayliffe, G.A.J. (Eds.), Principles and practice of disinfection, preservation and sterilisation, 2nd ed. Blackwell Scientific Publications Ltd., Oxford, England, pp. 557-572
- Lach, V.H. (1990) A study of conventional formaldehyde fumigation methods, J Appl Bacteriol. ;68(5):471-7
- Ackland, N.R., Hinton, M.R., and Denmeade, K.R. (1980) Controlled formaldehyde fumigation system, Appl Environ Microbiol.;39(3):480-7
- Hall, L., Otter, J.A., Chewins, J. and Wengenack, N.L. (2007) Use of hydrogen peroxide vapor for deactivation of Mycobacterium tuberculosis in a biological safety cabinet and a room, J Clin Microbiol.;45(3):810-5
- Chapuy-Regaud, S., F. Duthoit, L. Malfroy-Mastrorillo, P. Gourdon, N. D., Lindley, and Trombe, M. C. (2001) Competence regulation by oxygen availability and by Nox is not related to specific adjustment of central metabolism in Streptococcus pneumoniae. J. Bacteriol. 183:2957–2962
- Krause, J., McDonnell, G., & Riedesel, H. (2001). Biodecontamination of animal rooms and heatsensitive equipment with vaporized hydrogen peroxide. Contemporary Topics, American Association for Laboratory Animal Science, 40(6), 18-21
- Puskar, M.A. and Plese, M. R. (1996) Evaluation of Real-Time Techniques to Measure Hydrogen Peroxide in Air at the Permissible Exposure Level, American Industrial Hygiene Association Journal, Vol. 57, pp.843-848
- Unger-Bimczok, B., Kottke, V., Hertel, C., Rauschnabel, J. (2008) The Influence of Humidity, Hydrogen Peroxide Concentration, and Condensation on the Inactivation of Geobacillus stearothermophilus Spores with Hydrogen Peroxide Vapor, Journal of Pharmaceutical Innovation 3(2):123-133
- Drinkwater, J. and Buck, L. (2012). Gaseous Disinfection of Barrier Systems. In Sandle, T. (Ed.) The CDC Handbook: A Guide to Cleaning and Disinfecting Cleanrooms, Grosvenor House Publishing: Surrey, UK, pp198-240
- Khorzad D. (2003). Design and Operational Qualification of a Vapor-Phase Hydrogen Peroxide Biological Indicator Evaluator Resistometer Unit. Pharm Technol: 27(11):84–90
- Rickloff, J. and Orelski, P. (1989) Resistance of various microorganisms to vapour phase hydrogen peroxide in a prototype dental hand piece/general instrument sterilizer, in Abstracts of the 89th Annual Meeting of the American Society for Microbiology (American Society for Microbiology, Washington, DC, USA, 1989), abstract Q-59, p 339.
- Ohresser, S. Griveau, S. and Schann, C. (2004). Validation of Microbial Recovery from Hydrogen Peroxide-Sterilized Air, PDA Journal of Pharmaceutical Science and Technology, 58 (2): 75-80
- Akers,J.. Agallaco, J. and Kennedy, C. M. (1995) Experience in the Design and Use of Isolator Systems for Sterility Testing, PDA Journal of Pharmaceutical Science and Technology, 49 (3): 140-144
- Anon. (1998) National emission standards for hazardous air pollutants for ethylene oxide commercial sterilization and fumigation operations--EPA. Interim final rule, Fed Regist. 1998 Dec 4;63(233):66990-4.
- Shirasaki, Y., Matsuura, A., Uekusa, M. , Ito, Y. and Hayashi, T. (2016) A study of the properties of chlorine dioxide gas as a fumigant, Exp Anim. 29;65(3):303-10
- Lowe, J.J., Gibbs, S.G., Iwen, P.C., Smith, P.W., and Hewlett, A.L. (2013) Decontamination of a hospital room using gaseous chlorine dioxide: Bacillus anthracis, Francisella tularensis, and Yersinia pestis, J Occup Environ Hyg.;10(10):533-9
- Korich, D. G., J. R. Mead, M. S. Madore, N. A. Sinclair, and C. R. Sterling (1990). Effects of ozone, chlorine dioxide, chlorine and monochloramine on Cryptosporidium parvum oocyst viability. Appl. Environ. Microbiol. 56:1423-1428