Fumigation of Safety Cabinets

Transcription

1 Fumigation of Safety Cabinets General Microbiological safety cabinets should always be fumigated if a large spillage of infectious material occurs within them, before filters are changed or before any maintenance work is carried out which involves gaining access to the interior of the cabinet (for example air ducts). On occasions it may also be necessary to decontaminate laboratories or animal containment facilities when, for example, there has been a major spillage of infectious material or when certain servicing or maintenance work is to be carried out. Fumigation with formaldehyde vapour is the recognised and most commonly used method for this type of fumigation procedures although an alternative system using vapourised hydrogen peroxide is available. Since the latter is not in common use within the University, and the cost of the equipment is such that it is not likely to become so, it is not considered further here. Under no circumstances should any other type of fumigant be used for fumigation of laboratories, rooms or microbiological safety cabinets. Formalin is a commercially available 40% solution of formaldehyde vapour in water. When formalin is heated formaldehyde vapour is generated in quantity. Formaldehyde is a Schedule 1 chemical under the COSHH Regulations and has a Maximum Exposure Limit (MEL) of 2 ppm (or 2.5 mg.m -3 ). Concentrations encountered during fumigation are many hundreds of times higher than this so fumigation operations must be carried out only by trained personnel under strictly defined conditions. All workers using formaldehyde must be aware of safe handling procedures. Under certain conditions formaldehyde can react with hydrochloric acid and chlorine-containing disinfectants such as hypochlorites to form bis (chlormethyl) ether, a potent lung carcinogen. Hydrochloric acid and chlorinecontaining disinfectants must therefore be removed from rooms and microbiological safety cabinets before fumigation. Formaldehyde vapour is an extremely effective biocidal agent. It acts as an alkylating agent, inactivating micro-organisms by reacting with carboxyl, amino, hydroxyl and sulphydral groups of proteins as well as amino groups of nucleic acid bases. A number of factors effect the efficiency of fumigation. For formaldehyde to act to maximum effect it must be able to penetrate (precleaning is helpful if it can be done without jeopardising safety) and it must be able to dissolve at adequate concentrations in a film of moisture in the immediate vicinity of the organisms to be inactivated. Water vapour generated in the process of dispersing formaldehyde provides the essential optimum level of relative humidity and so it is important to ensure that water is added to the formalin prior to vapourisation. Too much formaldehyde results in the deposition of sticky deposits of paraformaldehyde and in cabinets may contribute to filter blockage. The amounts of formalin and water required for fumigation are given in the more detailed sections below. Fumigation is most Created on 20/07/2009 Page 1 of 8

2 effective above a temperature of 20 o C and relative humidity of 65%. At temperatures below 18 o C formaldehyde fumigation is less effective. Below 9 o C, formaldehyde sublimes and is less easy to vaporise. Agents causing the transmissible spongiform encephalopathies are resistant to inactivation by formalin and so its use is not appropriate in these cases. Workers handling these types of agents should ensure alternative decontamination procedures are put in place in advance of any work commencing. Further advice can be obtained from the University Biological Safety Adviser. There are a number of methods of generating formaldehyde vapour: heating a mixture of formalin and water in a thermostatically controlled heating unit such as an electric frying pan (electric kettles are not ideal as some formalin is left beneath the element) or a purpose-made vaporising unit; using commercially available formaldehyde generating kits; or mixing formalin and water with potassium permanganate crystals*. *WARNING: the correct relative concentration of these two components is essential to avoid a violent reaction. It is therefore recommended that this method is NOT used. Fumigation of microbiological safety cabinets Microbiological safety cabinets, if they have been used for hazardous microorganisms, must be fumigated in the following circumstances: After a major spillage or a spillage where inaccessible surfaces have been contaminated; Before any maintenance work on the cabinet where access to potentially contaminated parts is necessary (including filter and prefilter changes); Before carrying out filter penetration tests; and When there are any changes in the nature of the work that result in significantly different risks. Fumigation must be carried out only by a trained responsible person with adequate knowledge of the procedure and the precautions to be followed. Where the cabinet has been used for hazardous micro-organisms, HEPA filters should be handled only with appropriate protective clothing (laboratory coat and heavy duty gloves) even after fumigation. Such filters must either be autoclaved prior to disposal in the general waste stream or be securely wrapped in yellow bags for disposal as clinical waste. The cabinet must be sealed before fumigation to prevent leakage of formaldehyde into the laboratory. It should be checked to ensure that the closure panel/night door has been properly and securely located and a good Created on 20/07/2009 Page 2 of 8

3 seal has been achieved. Where necessary sealing tape should be used to ensure there is no leakage. With Class III or hybrid (Class I/Class III) cabinets a blanking plate should be fitted over the inlet filter. If the cabinet is a recirculation type, there must be a safe means of venting the formaldehyde vapour to atmosphere (the outside) such as by the use of a fumigation adaptor kit (see below). This must be fitted to the cabinet prior to commencing fumigation. The fumigation procedure should ensure inactivation of any micro-organisms that have penetrated the HEPA filter by adequate exposure of the downstream side of the HEPA filter and the ductwork to formaldehyde. In the absence of specific recommendations by the cabinet manufacturer the cabinet fans should be turned on for seconds after about half the formalin has been evaporated and again after evaporation is complete. Passive migration of the fumigant through the filter can occur but this is not ideal. Some cabinets have automatic fumigation cycles programmed into the controls and in these instances the manufacturers' instructions should be closely followed. The formaldehyde should be left to disperse within the cabinet for at least six hours (or preferably overnight) after which time the fumigant should be exhausted to atmosphere by switching on the fan and allowing air from the room to enter the cabinet. Before venting the formaldehyde in this way it is essential to ensure that no-one is in the vicinity of the exhaust outlet and that the exhaust air does not enter nearby windows or ventilation air intakes. Following decontamination, the microbiological safety cabinet must be purged of all residual formaldehyde. With recirculation type cabinets a fumigation adaptor kit should be fixed over the cabinet exhaust to allow discharge of fumigant via the flexible trunking into either a ducted cabinet, fume cupboard, a fumigation port or out of a window. Care must be taken to ensure no formaldehyde is discharged back into the laboratory. Under no circumstances should recirculating type cabinets be fumigated unless there is a safe means for discharging the formaldehyde to the outside atmosphere. Formaldehyde must not be recirculated into the laboratory, this would constitute an uncontrolled release of a hazardous chemical and be a reportable incident to the Health and Safety Executive. In the event of investigating such an incident, or if during a visit, Health and Safety Executive Inspectors became aware that such an unsafe practice was in use, it is very likely that enforcement action would be taken and a successful prosecution be brought against the University. The quantity of formalin required is approximately 2 ml per cubic foot (0.028 m 3 ) internal air space. Typical quantities of formalin required for fumigation of the different types of cabinets are: Created on 20/07/2009 Page 3 of 8

4 Cabinet Type Amount of BP Formalin Amount of water Class II (1200 wide) 25ml 25ml Class II (900 wide) 20ml 20ml Class II (1800 wide) 30ml 30ml Class I 20ml 20ml Class III 20ml 20ml Class I/III Hybrids 20ml 20ml Whilst fumigation is in progress a large notice must be posted on the front of the cabinet to warn that the cabinet is being fumigated. An example of a suitable sign is provided below. Manufacturers of microbiological safety cabinets should provide detailed instructions for fumigation of their particular cabinets and these should be followed. This is particularly important when the cabinet has an automatic fumigation cycle. An outline of the main principles of fumigation has been provided above and manufacturers' instructions should be consistent with these (if there are serious discrepancies please contact the University Health and Safety Department for advice). Within Schools there must be a written procedure in place for cabinet fumigations. A summary of the main steps is provided below. This summary is a model only and should be modified as appropriate to tailor it to the particular cabinets in a laboratory. The written procedure must identify those individuals competent and authorised to carry out the fumigation process. 1. Switch off the cabinet fans. 2. If the cabinet is a recirculation type, fit the fumigation adaptor kit to the discharge and position the other end to vent to atmosphere. Close the manual shut-off damper. 3. Fill the vaporiser with the correct amount of formalin and screw on the aluminium cap - finger tight, having checked the gasket in the cap is undamaged. Place the vaporiser in the cabinet. 4. Fit the closure panel/night door and fully seal the front screen and closure panel with sealing tape to ensure there are no leaks. 5. Post a notice on the front of the cabinet indicating fumigation is in progress. 6. Switch the vaporiser on. 7. After approximately 10 minutes switch the cabinet fans on for seconds. 8. After a further minutes switch the cabinet fans on again for seconds. 9. Leave the cabinet in this condition preferably overnight, but for a minimum of 6 hours. 10. 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. 11. Before venting the formaldehyde check no-one is in the vicinity of the exhaust outlet and that gas will not enter any open windows nearby. Created on 20/07/2009 Page 4 of 8

5 12. 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. 13. Any poly-formaldehyde residue in the vaporiser may be removed be heating with water containing a little mild detergent. 14. Run the cabinet for at least a further minutes to remove the last traces of formaldehyde. 15. If the cabinet is a recirculation type the fumigation adaptor kit must be removed before the cabinet is used again. Fumigation of laboratories/rooms Formaldehyde fumigation of laboratories or other rooms must be carried out only by named trained personnel. Fumigation procedures for Containment Level 3 facilities must be validated to demonstrate decontamination efficacy. This involves undertaking a test fumigation with spore strips being placed at strategic locations around the laboratory. Before commencing fumigation the laboratory/room must be completely sealed to prevent escape of formaldehyde vapour into other areas. Containment Level 3 laboratories are designed so that they are easily sealable for fumigation with minimal effort. In other laboratories/rooms that have not been designed to facilitate fumigation it will be necessary, before commencing fumigation, to seal service ducts and other holes through which fumigants may escape. If the laboratory has a false ceiling the void above must be checked to ensure that there is no interconnecting ducting to other areas and if there is these must be effectively sealed. There must also be an effective means of venting the formaldehyde after fumigation. Given the difficulties associated with fumigating such a room, any plan to undertake a fumigation must be carefully considered, fully justified, risk assessed and have detailed written procedures in place. Schools are advised to discuss any proposal to fumigate a room or area other than a Containment Level 3 laboratory with the Health and Safety Department. Prior to undertaking a fumigation with formaldehyde vapour, it must be thoroughly checked and confirmed that the room is properly sealed and there will be no release of gas to other areas. Any such escape of formaldehyde would constitute an uncontrolled release of a hazardous chemical and be a reportable incident to the Health and Safety Executive. In the event of investigating such an incident, or if during a visit, Health and Safety Executive Inspectors became aware that the room had not be checked for leakage prior to fumigation, it is very likely that enforcement action would be taken and a successful prosecution be brought against the University. There must be a means of exhausting the formaldehyde vapour from the laboratory/room that avoids the need for any person to enter the area where the formaldehyde has been released. The extract must be a total loss system with no possibility of formaldehyde being ducted to other areas. This could be Created on 20/07/2009 Page 5 of 8

6 by the use of a ducted microbiological safety cabinet to exhaust the fumigant to atmosphere and via room extract ductwork. The recognised method is to have a switch external to the room to allow extraction of the formaldehyde without entering the room. The University Health and Safety Department must be consulted before any other method is adopted. It should also be possible to operate, without entering the room, any dampers that may be installed if their opening is necessary to ventilate the room. Once the formaldehyde has been generated the door must be locked to prevent anyone entering the room until the fumigant has been exhausted. Under no circumstances should anybody be allowed to enter a room whilst fumigation is in progress unless they are wearing full breathing apparatus that provides air from an independent source and they are fully trained in its use. Cartridge respirators are not appropriate for use in the concentrations of formaldehyde generated during fumigation. Calculations should be undertaken to estimate how long it will take to purge all the formaldehyde from the room after fumigation is complete. This should be based on room volume and the rate of air extraction through the particular exhaust system that will be used. The calculation should also take account of the initial formaldehyde concentration in the room and the need to reduce it to well below 2 ppm. The following formula can be used: room volume (m 3 ) time (mins) X25 = extraction rate (m 3.min -1 ) If a microbiological safety cabinet is being used to ventilate the room check the exhaust rate with the particular manufacturer. A Class II cabinet typically exhausts approximately 125 l.sec -1 (to convert l.sec -1 to m 3.min -1 multiply by 0.06). After fumigation the level of formaldehyde remaining in the air MUST be below 2 ppm (2.5 mg.m -3 ) before anybody is allowed to re-enter the room. The level of formaldehyde should be checked by, for example, sampling the air through a small port fitted in the door for this purpose. This can be done with either a hand-held direct reading instrument (such as a formaldameter) or appropriate air sampling tubes. If this sampling indicates levels are satisfactory to proceed (ideally less than 0.5 ppm) then further tests should be undertaken by a person entering the room to check the formaldehyde levels in all areas (often there are pockets of gas remaining following fumigation), this person must wear a laboratory coat, gloves and a full-face cartridge respirator (mask). Anyone wearing such a respirator should be aware of the level of protection afforded by it. As an example, a Class 1 full-face mask to EN136 (e.g. 3M 6000 series) with formaldehyde filters (e.g. 3M 6075 A1+formaldehyde) will protect up to 10ppm. The COSHH Regulations require that persons wearing full-face masks be subject to individual, and product specific, face-fit testing using a recognised quantitative test method. Further advice on this can be obtained from the University Occupational Hygienist and Safety Adviser. Created on 20/07/2009 Page 6 of 8

7 An outline of the main principles of fumigation has been provided above. The following is a summary of the main steps but this should be tailored to the particular laboratory or area to be fumigated. 1. Before commencing fumigation switch off all forced air ventilation systems, extract systems and any fume cupboards and microbiological safety cabinets in the room and deactivate fire alarm system smoke detectors. Seal up any external ventilation grilles as necessary. 2. Check that the point from which the formaldehyde will be exhausted is free from obstruction and that the remote switch that will be used to exhaust the formaldehyde from the room is working (run the extract this way for at least 5 minutes then switch off). 3. If undertaking a routine or test fumigation place spore strips at strategic locations around the room, following fumigation these should be collected and incubated. If there has been an accident any access in to the laboratory should be restricted to an absolute minimum and so this need not be done. 4. Place the appropriate quantities of formalin and water mixture into the heater unit and when ready activate the heater and leave the room IMMEDIATELY. Use 100 ml formalin plus 900 ml water per 28.3 m 3 (1000 ft 3 ) of space. 5. LOCK THE DOOR and effectively seal around the edges with tape. 6. Display a notice in large type on the door such as the following: WARNING, DO NOT ENTER, FORMALDEHYDE GAS DECONTAMINATION TAKING PLACE 7. Other warning signs may be required in the surrounding areas. 8. After a period of NOT LESS than 12 hours (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 dampers if necessary). 9. Allow the room to purge for at least the time calculated as necessary to remove the formaldehyde. 10. Check levels of residual formaldehyde in the room with suitable air monitoring equipment (formaldameter or air sampling tubes). Only enter if the level of formaldehyde is below 2ppm and wear a laboratory coat, gloves and a full-face cartridge respirator (with appropriate filter for formaldehyde gas). 11. Check the room and all surfaces for formaldehyde residues and clean up as necessary. 12. Remove all sealing materials. 13. Only allow other staff to enter the room when formaldehyde levels are below 0.5 ppm. Levels should be as low as practicable before staff reenter. A record must be kept of all fumigations of rooms/laboratories including date, personnel involved and the results of air monitoring on completion of the procedure. Biosafety Unit Health and Safety Department Created on 20/07/2009 Page 7 of 8

8 University of Edinburgh August 2003 Note: The information contained within these pages is for use by University of Edinburgh personnel only. If you wish to discuss any issues relating to the above documents please contact the University Biological Safety Adviser. Created on 20/07/2009 Page 8 of 8