Cleaning kitchen extraction systems plays an important role in any fire safety strategy.
A well-cleaned, maintained, and monitored kitchen extract system can provide the following benefits:
- Reduces the risk of grease extract system fires.
- Reduces the risk of spreading fires throughout grease extract systems.
- Contributes to providing a safe and hygienic area for food preparation.
- Provides a safer and more comfortable environment for kitchen staff.
- Keeps the system running in accordance with its designed performance.
The most important factor contributing to the safety of a kitchen extract system is regular and complete cleaning. The system should be cleaned at least every six months to remove grease and debris that can accumulate and cause fires.
As industries grow, national legislation and other stakeholders require that the risk associated with dirty kitchen extract systems is controlled. A modern, professional and technical approach is required to replace the well-intentioned amateur of the past. This approach brings areas of doubt into sharper focus, both for the specialist service provider and for the kitchen extract system user and other stakeholders.
This document seeks to clarify those areas of doubt and state what is expected from all parties about the correct risk management of kitchen extract systems and their use.
Contents:
INTRODUCTION
KITCHEN EXTRACT SYSTEM CLEANING
ELEMENTS OF THE DUCTWORK SYSTEMS
SYSTEM DESIGN AND ACCESS INTO DUCT INTERNAL AREAS
FREQUENCY OF CLEANING AND CONTROL OF FIRE RISK
CLEANING METHODS
CLEANLINESS VERIFICATION & REPORT
TRAINING AND COMPETENCE ASSESSMENT
HEALTH & SAFETY
INTRODUCTION
Grease and oil can build up on kitchen extraction (exhaust) systems, which can decrease their efficiency. No separator or filter device is 100% effective, so the rate of fouling varies. Other industrial cooking processes can also result in the buildup of grease and oil, which can be hidden inside ventilation systems.
Kitchen extract systems must be regularly inspected, tested, and cleaned to meet European and local safety regulations. It is important to keep these systems clean to minimise the risk of fires and other safety hazards. Various organisations provide guidance on how to best maintain these systems.
Grease and oil can spontaneously ignite at temperatures of 310- 360°C, which can cause a fire to spread rapidly through a system. If the grease levels have not been adequately controlled, flames and/or high temperatures can ignite the grease, causing fire to spread. Ductwork can also be heated to a degree that ignition of the surrounding materials can occur.
Fire Services and forensic fire investigators report many cases where a small kitchen fire has been spread well beyond the original seat of fire by grease-laden extract systems, causing major property damage well in excess of the initial fire.
Grease and oil fires can produce toxic fumes, including carbon monoxide (CO), hydrogen cyanide (HCN), and soot. Carbon monoxide is a colourless, odourless, and tasteless gas that is poisonous to breathe. It can cause death by reducing the amount of oxygen available to the body.
Hydrogen cyanide is also a colourless, odourless, and tasteless gas that is poisonous to breathe. It interferes with the ability of red blood cells to transport oxygen throughout the body. Soot particles are tiny and can lodge in the lungs, causing long-term respiratory problems.
Insurers are more attentive to specific cleaning requirements and proof of compliant cleaning maintenance regimes. If insurers cannot see that you are following the terms of your policy, they may refuse to pay out on any claims.
Insurers often base their requirements on cleaning frequencies, which can lead to excessively frequent cleaning, as well as insufficiently frequent cleaning. This article calls for Condition Based Maintenance to ‘clean only when systems are dirty’, defined by the Grease Thickness Test (Wet Film Thickness).
Accumulated grease can create a hygiene hazard, leading to foul odours, pest infestation, and unhygienic conditions. Leaks from damaged or improperly-installed ductwork can spread these hazards to other areas of the building, such as food preparation areas or service areas.
A Fire Risk Assessment should be conducted by a nominated competent person. This person should identify any potential hazards associated with kitchen extract ventilation, such as inadequate cleaning regimes. The findings of this assessment should be recorded and kept under review, particularly if there are any changes in the system, cooking practices or frequency of use.
EC852-2004 says that ‘Ventilation systems are to be so constructed as to enable filters and other parts requiring cleaning or replacement to be readily accessible.’ All parts of the ventilation system need access for interior cleaning.
KITCHEN EXTRACT SYSTEM CLEANING
A cooker hood or canopy is defined by CEN European Standards Committee as a device intended to collect airborne contaminants from above a cooking appliance. The system will typically include an extract fan and ductwork to convey the contaminants from the canopy to the fan. Kitchen extract systems take hot, greasy air away from the cooking area, making the kitchen tolerable and safe for people to work in. Airflow is typically created across the cooking process to capture the effluent and discharge it to the atmosphere.
Why clean kitchen extract systems?
Oil and grease vapours will escape into the air when cooking. Most extract systems have filters to capture most of the vapour, but it’s important to remember that no filter is perfect. Some of the vapour will escape through the extract system. The vapours will cool and condense on the ductwork in the kitchen, forming a layer on the surface.
This grease and oil can build up if left unchecked, leading to a fire hazard in the ductwork. As illustrated by the Fire Triangle below, three components are required for a fire to occur. In a ventilation system, there is plenty of oxygen; there is fuel and plentiful sources of heat energy. Spark, flame, or simply high-temperature air, adds the third dimension to complete the Fire Triangle. Oxygen from fanned air provides the beginnings of a turbo-fire (similar to the forced air-fed forge furnace), fanning the flicker of flames into an uncontrolled inferno.
To mitigate the potential for a fire in the ductwork, it is important to have a scheduled maintenance program that includes cleaning and inspecting the ductwork for grease and oil build-up.
The build-up rate of fat and grease in ductwork systems will vary depending on the amount and type of food being cooked. It is important to clean and audit ductwork systems regularly to prevent a fire hazard.
How to Reduce the Risk of a Kitchen Extract System Fire
There are several things you can do to reduce the risk of a fire in your kitchen:
- Regular cleaning and maintenance of your kitchen extract system can help prevent the accumulation of grease and oil.
- Make sure the ductwork is properly sealed and insulated. Leaks can allow flammable vapours to escape and spread the fire.
- Install a smoke detector in the kitchen and test it regularly.
If there is a fire in the kitchen, evacuate the building immediately and call 999 (112). Do not try to fight the fire yourself.
Extract systems in kitchens have the potential to accumulate grease and oil, creating a dangerous fire hazard. If these deposits ignite, the fire can spread quickly through the ductwork and throughout the building. It’s important to be aware of this danger and take precautions to protect yourself and your property.
We have estimated that fires caused by dirty kitchen extract systems cause insurance losses of €447 million across the European Union. The economic damage to property and businesses is large enough that we need to take steps to minimise these losses. The risk to human life – especially when considering buildings where sleeping accommodation is provided above commercial kitchens, e.g. hotels and city centre apartment blocks – cannot be ignored.
ELEMENTS OF THE DUCTWORK SYSTEMS
Grease or kitchen extract ductwork is usually made from steel, typically galvanised sheet steel in a rectangular or spiral-wound circular format, but can also be made from all-welded ‘black iron’ or stainless steel.
A kitchen extract system would typically consist of ductwork plus some of the following components:
Extract Canopy or Hood
An extract system is made up of a series of parts, including the skirts that direct airflow to the extraction point. This section is most easily accessible and is usually cleaned frequently by kitchen staff.
Canopy grease filters (Separators)
All types of filter/separator can be fitted to the extract canopy as the primary or secondary point of grease capture. Grease filters/separators should be regularly cleaned (often daily/weekly) to remove grease deposits.
Canopy extract plenum
This is the area below where the ductwork is connected and behind the grease filter housing. This area can accumulate high levels of grease quickly. It may have removable traps or drainage points.
Fire dampers
Kitchen extract systems should ideally not have fire dampers as they interrupt airflow. Grease can accumulate at the damper and make it inoperable. In some countries, fire dampers are allowed by local design codes. They are also occasionally found in older or non-compliant systems.
Sound attenuators
Baffles contain a sound deadening material (typically man-made mineral fibre) held in place with a scrim covering and typically metal panels that have circular holes cut into them to allow the fan noise to be absorbed. If the internal filling becomes saturated with grease, any remedial work will not form part of a typical cleaning contract.
Turning vanes (change of direction)
While it’s not always considered to be the best design practice, sometimes you will find turning vanes in the ductwork. They are used to help smooth and direct the flow of air. However, you should avoid using turning vanes wherever possible because they create a disturbance that can form a grease accumulation point. Radius bends for changes in direction are preferable.
Volume Control Dampers (VCD)
In-line components used to regulate and control airflow volumes to the system should not normally be found in a system designed to best practice. However, if found, the set position should be carefully noted and returned to position, before and after maintenance.
Extract fans
I cannot tell you the best kind of fan to get for your kitchen extraction because it depends on the specifics of your system. What I can tell you is that it is important to clean your fan regularly, as this will help it run more efficiently and last longer. There are three main types of fans – centrifugal, axial, and bifurcated – so take a look at the images below to see which one might be best for you.
Centrifugal fan
Centrifugal fans are very common and powerful. They use an outside air stream to create a centrifugal force that pushes the air through the fan blades. This type of fan is ideal for kitchen extract systems, as they work well with components that have high resistance and changes in direction. Systems with grease treatment and multiple changes of direction usually have centrifugal fans fitted.
Axial fan
Axial fans are the most common type of fan found in kitchen extract systems. The motors tend to get dirty quickly and they can be difficult to fit. They also make a lot of noise and the blades tend to collect grease, which can lead to spinning imbalances and fan failure.
Bifurcated fan
Bifurcated fans are less common because they are more expensive to produce. They are often found in factories and production lines, where the cooking duration and temperatures are higher. Unfortunately, access to the internal surfaces of the side chambers for maintenance is often difficult, and plates (which are supposed to be there for this purpose) are often not provided.
Ratings for kitchen extract fan motors
Electrical equipment such as motors in fans often have an Ingress Protection (IP) rating which tells how resistant it is to foreign bodies such as dust, fluid, and moisture. The first number indicates resistance to solids, graded from 1-6. The second number indicates resistance to liquids, graded from 1-8. To be confident a fan will not be damaged by chemical cleaning, a rating of IP55 or greater is needed.
Discharge duct
A discharge duct on the exhaust side of the fan would direct extract air out of the building. The outlet point may have louvres and mesh to prevent the ingress of windblown waste, leaf litter, precipitation and vermin. There may be a vertical discharge cowl and rainwater drain, as per the design illustrated here.
Ultraviolet (UV) systems
UV or similar systems within the grease extract canopy and ductwork system may help to reduce the accumulation of grease. However, a full system inspection will still be required to determine the appropriate cleaning frequency. It should be noted that ‘no filter system is absolute’ and all filtration, separation or treatment systems will let a quantity of grease through. When working on UV systems, interlock systems should be identified to ensure the safe isolation of the UV systems before maintenance or inspection.
UV systems should be isolated and purged before maintenance in order to avoid exposure to elevated ozone levels and light frequencies that can be hazardous to the eyes. UV systems are commonly mounted within the canopy plenum or further downstream in the ducted system as separately manufactured units. These require specialist competencies for maintenance and cleaning.
Water Wash canopies and Continuous Cold Water Mist systems
Water-based systems can be used to clean the inside of canopy voids and also act as a filter. Misting systems can be used in areas where there is a lot of solid fuel cooking, as they help prevent sparks from spreading.
Fryer ranges
Extractor hoods are commonly found in fast food frying premises. They often have internal ductwork that links to a section of extract ductwork and a sump beneath the floor.
Carbon filtration/separation
There are technical arrangements that filter odours at a molecular level. In order to avoid clogging of the carbon beds, these arrangements require high-efficiency particulate filtration upstream. They are typically installed before discharge in order to minimise the release of odours in compliance with local planning requirements.
Electrostatic precipitation separators (ESP)
Separators in electrically charged separator banks, fitted to minimise system atmospheric discharge, require regular cleaning or ‘laundering’ to maintain efficiency.
Grease & odour treatment systems
There are systems that can be used to reduce grease and odour nuisance. These systems use ozone or ‘Trioxygen’ to destroy odour components and grease particles. It is important to disable the ozone injection during cleaning and maintenance work.
Gas interlock systems
There is sometimes a ventilation system interlock to the gas supply serving the cooking equipment. This is installed so that if there is a failure in the airflow, the gas supply will be cut off, to reduce the risk of carbon monoxide and other combustion products entering the kitchen workplace. It’s important to reset the interlock to allow cooking after maintenance operations, such as cleaning.
Pitot Air Flow Tubes
Pitot tubes are small tubes that penetrate the ductwork and are linked to pressure switches. These switches transmit to the Building Management System (BMS) or safety system. They are critical to the kitchen range function and can be easily damaged or blocked during maintenance. The presence and location of pitot tubes should be identified by the installer and clearly marked on the as-installed drawings.
Recirculation systems
Regular inspection and maintenance of the separation or ‘filtration’ fitted to the system is required to control contaminants being re-circulated into the internal environment. These require specialist competencies for maintenance and cleaning.
High temperature flues / ducts
There are many types of solid fuels and gas applications that can be used for high-temperature cooking processes, such as pizza ovens. These ovens often utilise high-temperature insulated or twin wall ducts/flues to achieve the desired results.
Ventilated ceilings
To keep your full-ventilated ceiling system running smoothly, you’ll need to periodically remove the extract cassettes and clean the non-drip integral or perimeter troughs and the relevant void areas above them. It’s important to note that many designs require cassettes to be replaced in the same position so as not to disrupt the airflow pattern. Systems with ventilated ceilings that are connected to pizza ovens and fish frying ranges require the same cleaning considerations as ductwork.
Solid Fuel Extraction systems
There are many different types of fuel-based cooking systems, and each one has its own set of challenges. For example, charcoal and wood-fired systems need special airflow and fan operation in order to function safely.
Additionally, carbon monoxide build-up must be monitored vigilantly, as this gas is odourless and highly toxic. It’s important that these systems remain clean, as sparks can easily enter the ductwork and cause a dangerous fire. The US NFPA Standard 96 recommends monthly inspections of all fuel-based cooking systems.
Control Measures and Devices
The kitchen environment might have devices installed to reduce the spread of fire into the ductwork such as a fire suppression system or fire dampers. Some ductwork systems have the suppression arrangement linked to the extract fan. When the suppression system is triggered, the fan stops running.
Fire suppression systems
Component parts of a fire suppression system include the fusible link actuation mechanism, the nozzles, the piping, and the control cabinets. These systems use a wet chemical agent to put out fires. Most fire suppression system suppliers and their maintenance agents will not allow third parties to carry out any kind of work (including cleaning) on their systems. They will threaten to deny the warranty if third parties ‘touch’ their systems. Many insurers accept this restriction on behalf of their clients (e.g. restaurants). Specialist cleaning contractors have the training and equipment necessary to clean fire suppression systems without compromising their integrity.
The contractor faces several risks while doing the job:
- He may accidentally discharge the suppression system
- He may isolate the system and then fail to re-arm it upon finishing the work c. He may damage the system so that it will not operate at all
- He may alter the system so that it does not operate perfectly (as set up by the specialist installer/maintainer) e.g. by changing the direction nozzles point.
Unfortunately, this can often leave specialist contractors feeling forced to exclude any cleaning from the contract (and to make that clear in their Post-Clean Report). They may also require the client to arrange for safe isolation and subsequent reinstatement of the fire suppression system. This is often not satisfactory to the client, as it is likely to involve an incomplete job and/or extra expense to call out a fire suppression system engineer at the beginning and end of the cleaning job.
The specialist cleaning contractor should discuss with their client what their stance is on this restriction, then clearly outline in their offer what is and isn’t included. One solution may be for cleaning contractors to become trained in safe work practices around fire suppression systems, improving service for clients. This may require cooperation from local fire suppression system representatives.
SYSTEM DESIGN AND ACCESS INTO DUCT INTERNAL AREAS
There is no one-size-fits-all answer to the question of ventilation in commercial kitchens; the right solution depends on the specific kitchen layout and requirements. However, EN 16282:2017 – “Equipment for commercial kitchens. Components for ventilation in commercial kitchens” – provides a good starting point, and local/national design or specification guidance such as BESA DW172, VDI 2052 can offer more detailed advice.
There are several important design features that are common in almost all kitchen design guidance:
- Ductwork routes should be as short as possible in order to minimise grease accumulation and fire hazards.
- Short vertical runs are the safest because less grease accumulates there.
- Changes of direction should be minimised to avoid grease accumulation and fire hazards.
- Turns and bends are locations where grease can accumulate, and also where fire/ hot air/gases are concentrated.
- Internal surfaces should be smooth to prevent leakage of grease vapour
The most important thing to remember when cleaning convenience store ductwork is that all internal surfaces must be accessible. Unfortunately, sometimes design, installation, and construction processes are not perfectly coordinated, which can lead to the following problems: Access panels installed by the installer may be too small or obscured by other services. There is no safe access to roof-top fans and discharge grilles/louvres etc.
To ensure that ductwork can be properly cleaned, building/system owners and operators should take care not to block access panels with alterations, furniture, equipment, or partitioning. If access panels become inaccessible, a specialist duct cleaning contractor may need to replace them.
Access panels
A kitchen extract ductwork system, canopy and extract plenum should be fitted with access panels that allow for regular cleaning and inspection of the internal surfaces and in-line components.
The European standard EN 12097:2006 specifies the requirements for ductwork components that make cleaning easier, but it does not address the specific needs of grease-affected kitchen extract systems. The standard requires that access panels be designed and installed in a way that makes cleaning possible, but this is often not adequate for kitchen extract systems. For example, the requirement that access panels be installed every 7.5 metres is usually insufficient for cleaning purposes.
Location of access panels
There are a number of design and operational factors that need to be considered when setting up a commercial cleaning ductwork system:
– The location and design of the ductwork
– The materials used in the building’s construction – Additional builders’ work hatches may need to be fitted in the ceilings and/or walls of existing installations or be provided for in new constructions. Note that these would not normally be provided by the cleaning contractor unless specified and priced separately.
Location of the kitchen within a building is important for both the efficiency of the kitchen and for safety reasons. The extract fan should be located near the cooking area to remove smoke and fumes, and it should be easy to access for maintenance.
The design of the fan should allow for thorough cleaning of the impeller blades and internal surfaces without having to take the fan apart. Larger fans should have panels in the casing that allow hand access to the impeller blades.
Similarly, in-line fittings that obstruct cleaning must have easily removable access panels on both sides. Accessibility to the ductwork (exterior) is important for physically reaching the ductwork.
Bespoke permanently fixed access gantries or platforms may be required above ceilings to enable safe access to cleaning access doors for high-level working.
Building modifications and current uses that restrict access must be taken into consideration when planning the system layout.
Location and number of system components requiring access must also be considered when designing the cleaning system.
Suitability of access panels
Access panels should be made of a material that is similar to the ductwork. They should have quick release mechanisms and sealing gaskets, as well as fire-resistant, thermal, and acoustic properties.
Fire-rated ductwork
It is important to take care when maintaining fire-rated ductwork. The manufacturer or specialist fire protection advisor’s recommendations must be followed, and the fire resistance of the ductwork must be recertified after any work that involves installing access panels.
Additional access panels
Any duct work or panels should be as large as possible without weakening the overall structure, and any access points (such as panels or apertures) must be clear of any obstructions. There should be no sharp edges on any of these features.
Fitting location
Access panels should be fitted to the side of the duct at a minimum of 10mm above the base to reduce the risk of leakage. In exceptional circumstances, they can be fitted on the top or underside of the duct to enable access. In either case, due consideration must be given to the accessibility of the panel.
Leak-free positioning
When fitting access panels to the underside of a duct, it is important to ensure a leak-free fit. A sign should be affixed to the panel warning of the risk of oil release when the panel is opened.
Access to ductwork and access panels.
Staff need to access and clean all access panels. This may require the specifying of permanent working platforms to enable safe working access during each cleaning operation. Other services which may be installed after the original installation of the extract ductwork, such as architectural features and building fabric should not obstruct any access panels. Equally, any kitchen equipment installed below duct access panels must not restrict access for cleaning purposes. If necessary, kitchen equipment shall be easily movable on flexible services connections.
Location of access panels.
All internal surfaces of the ductwork should be accessible for cleaning, typically through manual means. Panel should be fitted on either side of in-line components to enable cleaning of components and nearby ductwork. Components such as fire dampers and attenuators are included in the table as they are often installed, even if not recommended.
Panels need to be installed at least every 2 metres to enable arm’s-length cleaning. If the duct size (typically: if it is very small) limits hand-cleaning, or if other external features restrict the positioning of panels, then more frequent access may be required.
At the design stage, consideration should be given to the provision of safe access to the downstream side of discharge grilles, bird guard mesh and louvres. Attenuators should also be given special consideration for access, such as easy removability.
The installer should specify the locations of, and sizes for, access doors to ensure full safe access for cleaning inspection and maintenance at the point of handover. Specialist cleaners may be invited to approve a new installation and deem it as clean-able.
Ductwork supports
According to EN 12236: ‘Ventilation for buildings – Ductwork hangers and supports Requirements for strength’, designers must consider insulation loads, imposed loads (cleaning and maintenance), vibration isolation, and corrosion resistance when designing hangers and supports. This is necessary to ensure the strength of the ductwork system.
“The additional weight of a person or persons who may gain access to the ductwork for purpose of cleaning or maintenance.”
Manufacturers recommend that ductwork, fasteners, suspension systems and fixings to building structures be capable of a point load of a minimum of 102 kg. However, cleaning specialists should always assess the risk of duct collapse before imposing a load on ductwork by e.g. entering or leaning on it.
FREQUENCY OF CLEANING AND CONTROL OF FIRE RISK
This guide provides advice on how to minimize the accumulation of combustible materials near kitchen extraction systems, in order to reduce the risk of fire.
Cleaning a system only when it is visibly dirty is less effective and economical than cleaning it on a condition-based maintenance schedule.
Time-based cleaning may not be frequent enough for very dirty systems or too frequent for lightly used systems. In the absence of other information, all kitchen extract ductwork systems should be cleaned at least once a year.
Property owners, system designers, and insurance providers may have specific cleaning intervals in mind which must be complied with in order to maintain the validity of the policy or lease agreement. It is the responsibility of the owner/operator to ensure that these requirements are communicated to the cleaning and maintenance contractor. A professional duct cleaning contractor should be able to identify unclean areas during inspections.
This guide advocates maintenance that is based on the condition of a system. A system should be cleaned when it is dirty, and the frequency of cleaning should be sufficient to ensure that it does not become dirty. Cleanliness and dirtiness are defined by means of measuring the thickness of grease deposits, using a Wet Film Thickness gauge.
Cleaning frequencies should be based on the historical levels of grease accumulation in order to maintain grease thickness levels below 200 µm. Exceeding these levels would “trigger” a cleaning requirement.
Some ductwork may have grease levels that exceed 500 µm, which is known as a “hotspot” or “high point.” These areas need to be cleaned as soon as possible, but it’s important to consider how dirty the area is at 500 µm and how much of a risk it poses. For example, if the grease level is 500 µm near the heat source, it would be a greater risk than a high point on a turning vane far from the heat source.
Interim cleaning of high-point areas should be introduced to the full system cleaning schedule if it is deemed necessary in order to control the risk of ‘hot spot’ accumulation.
If there is no historical data for the deposit levels at newly installed systems, then time-and-usage-based methods must be used to estimate the starting cleaning frequency. See Table 4 which describes a Planned Preventative Maintenance regime based on time and estimated throughput (of grease from cooking).
There is no one-size-fits-all answer to how often a kitchen exhaust system should be cleaned. The frequency of cleanings will depend on how quickly grease builds up on the surfaces. If grease deposits reach a thickness of 200 µm or more, then it is time for another cleaning.
Before starting any cleaning procedure, it’s important to take fresh grease thickness readings. This will help you figure out how much the grease has grown since the last reading, and how often the cleaning should be done based on that rate. Gathering data this way is more accurate than relying on opinions or guesses.
If other factors that influence grease accumulation are known, such as peak periods of trade or where historical data exists, then interim inspections should be carried out to check grease thickness and further frequency adjustments made as appropriate. For example, some fast-food chains carry out a cleaning frequency based on turnover.
This approach provides a rational basis to minimise cost, intervention and disruptive visits while maintaining the required cleanliness and fire safety for the client.
The canopy and extract plenum are areas at a higher risk of fire. They will usually collect heavier deposits more rapidly and will need more frequent cleaning, either in-house or by a specialist service provider. A dedicated in-house cleaning regime usually keeps the more readily accessible canopies, separators, drains and traps clean.
CLEANING METHODS
There is no single method that is effective for cleaning kitchen extract systems. It is important to note that the skill and experience of the cleaning specialist are critical in ensuring that these systems are kept clean and safe.
The skill and management control required vary from relatively simple, like a stand-alone restaurant with a 1-metre section of duct rising to an accessible roof fan, to relatively complex, like a food court in a shopping mall where ductwork passes through various areas or rises to great height in a hi-rise building.
There are a few things to keep in mind when cleaning: often, more than one method is necessary to achieve cleanliness. For example, simple scraping might be followed by wiping or scouring/scrubbing. If a system has been neglected for a while, it might take multiple attempts to bring it back to its usual clean state.
The guidance in this publication on cleaning methods is not definitive. There are many methods and technologies that can be applied. It is important to stay up-to-date on the latest methods and technologies in order to effectively clean your building.
There are various methods that can be used to clean surfaces, depending on the type of grease and its condition. Generally, there are 5 types of grease: dry/hard burned-on, ‘varnish-like’, semi-dry, fluffy, semi-wet, and wet, liquid oil. The sooty type is common in oven extracts from pizza ovens and barbecues.
The time of day can affect the work that can be done due to noise concerns with some cleaning techniques and the length of time that is allowed for cleaning services. This can limit the types of work that can be performed.
When selecting a cleaning method, it is important to consider operative safety. This includes avoiding chemical skin burns and inhalation risks. Additionally, duct entry should be avoided wherever possible.
If you need to clean your ductwork, it’s important to do so in a way that doesn’t put it at risk. Remote chemical brushing, steam cleaning, and high-pressure water washing can all be dangerous if not done properly, so it’s important to assess the situation before getting started. Unless the ductwork is specifically designed for wet cleaning, there’s a good chance that water and chemicals will leak out and cause damage.
Ductwork systems should be designed and installed to comply with access door frequencies. This will reduce the need for mechanised cleaning, brushing of areas with no/limited access, and the use of wet cleaning and fluid removal from ductwork sections.
Wet cleaning methods may create condensed vapours and cleaning fluid residue which must be removed from all parts of the system.
There are pros and cons to both round and rectangular ducts when it comes to cleaning. In general, rotary brushes are easier to use in round ducts, while hand scraping is more difficult in smaller diameter ducts.
Rectangular ducts are more difficult to clean with a single brush, but this can be made easier with centering devices or swinging brushes that move from side to side.
When cleaning galvanised steel, be careful not to scrape or scrub too hard, as you might damage the galvanisation layer and expose the steel to corrosion. A high-pressure spinner can be an effective way of cleaning ductwork, especially if the water and grease sludge residue is contained. Hot water and chemical treatments can improve cleaning performance.
Cleaning ductwork can be difficult, but high-pressure spinners that direct water centrifugally away from the hose head can be an effective method, especially if the water and grease sludge residue can be effectively contained.
Hot water and chemical treatments can improve cleaning performance. However, chemical risk assessment must be carried out before using any cleaning agents to check their effects on the surfaces, cleaning staff, and environment. Some chemicals can damage system components such as aluminium and destroy sealants and gaskets on ductwork.
When cleaning greasy surfaces, it is important that the chemical agents have enough time to work. Foaming agents can help to give the chemicals more contact time and ‘scarifying’ or cutting up the grease layer can help the chemicals to penetrate to the metal surface.
There is no practical or measurable target for ‘back to metal’ when it comes to ductwork systems- that’s why the definition of cleanliness is defined as <50 µm residue. Over-aggressive cleaning can be economically impractical, dangerous and can damage ductwork and coatings designed to protect fans and other components of the system.
Most jurisdictions have some sort of legal waste disposal process in place. Normally, service contractors will dispose of waste in the client’s normal waste stream whenever possible. However, there is mounting pressure from the EU and local authorities to enforce specialist waste disposal or recycling.
If you need to have your ventilation or extraction system cleaned, it’s important that you be aware of any existing damage beforehand. This way, the contractor can be sure to avoid any further damage while they work. Be sure to document any damages found before work begins, so there is no confusion later on.
The client will be responsible for certifying that the fire resistance of the cleaned area remains intact/insulated. Only a few access panels should be removed at any given time. It is the responsibility of the cleaning contractor to make sure all access panels are properly replaced after cleaning. Any pre-existing cladding damage will not be fixed as part of this project.
CLEANLINESS VERIFICATION & REPORT
For verifying that a surface is clean, it should be visibly free of contaminants and able to meet the specified level of cleanliness. This should be verified with the Grease Thickness Test (GTT).
After cleaning, all post-clean Grease Thickness Tests should not exceed 50 µm and should be representative of the system. Pre- and post-clean grease measurements (GTT) should be taken from at least the following representative locations, where practicable, and detailed in the post-clean report.
There are several locations in the kitchen where grease accumulations should be noted and addressed, including:
– Canopy(s) extract plenum(s) behind filters
– Duct 1 m from each canopy
– Duct 3 m from each canopy
– Duct midway between canopy(s) and fan
– Duct upstream of fan
– Fan
– Discharge duct downstream of fan
The contractor who maintains the system has a duty of care and responsibility to let the client know of any fire risks they observed. If they did not clean the entire system, they must provide clear information about which sections were not cleaned and the reasons why.
They should also make recommendations for how to fully clean the system. This report should be submitted to the client within 30 days of the date of final cleaning attendance.
The nominated responsible person on site for the maintenance contractor shall be deemed to be the ‘signing off’ engineer and therefore holds the responsibility for clarifying the extent of the clean carried out. These individuals shall be qualified to a minimum of Grease Hygiene Technician standard or equivalent.
A Post Clean Report will include the following:
- An executive summary page that highlights the following key risks
– System was not clean in its entirety
– What was not cleaned and why not
– Suggested solutions and recommendations
- GTT readings for the stipulated test locations
- Other hazards that have been identified
Please be advised that there will be areas of the system that will not be cleaned as per our agreed upon pre-clean. The mean (average) micron reading across all GTT readings taken will determine the new cleaning frequency. Photos of the system must be provided before and after cleaning to confirm satisfactory results.
Images should be taken from an identical location, with the same level of zoom and angle. They should be taken from the centre of the duct, to give a good view upstream or downstream.
- Image files, including date and time information, should be made available to clients if requested.
- Images should also be taken to illustrate any hazards, access issues, system damage etc.
- A schematic diagram (see below) or, as-installed drawing, of the system layout showing the system in its entirety including known components
Drawings – update/create
If there are no as-installed drawings, access panels should be labelled and identified on a schematic sketch.
Schematic sketches can be very simple or very sophisticated, but the important thing is that the customer should be able to understand them.
For multi-site clients, the maintenance contractor will typically amalgamate all executive summary pages for each site into a review meeting summary schedule. This master summary should identify issues across the portfolio. It should be presented to the client as a minimum annually after completion of all initial cleans.
TRAINING AND COMPETENCE ASSESSMENT
Cleaning kitchen extract systems in hot, wet environments and using powered equipment, hazardous chemicals and cutting equipment carries significant risk which must be minimised by a suitable system of work.
Supervisors and operatives should be suitably trained and assessed to ensure that this work is carried out safely and with due regard to the wider environment.
Duct cleaning specialists should be safety-trained and competent in at least the following areas:
- Confined spaces – for full entry into a ventilation system or duct
- Working at Height – to work at height due to the nature of ventilation components being at high level or within ceiling voids
- Asbestos Awareness – to protect from exposure to hazardous asbestos materials which may be uncovered especially in ceiling voids, plant rooms etc
- Safe use and storage of chemicals
- Manual Handling – good practice and techniques for manual handling
A suitably trained supervisor or technician should be able to demonstrate knowledge of:
- Safe working practices
- The principles of kitchen grease extract systems and associated components
- Planning and preparing the work location
- Cleaning of kitchen grease extract systems and associated components
- Supervision
- Working sustainably
- Pre- and post-clean testing and reporting
He or she will be able to:
- Understand health, safety, and environmental requirements in the workplace
- Understand the principles of kitchen grease extract systems and components
- Safely prepare the work area for cleaning activities
- Select the correct materials, tools, and equipment for work
- Install suitable access panels
- Safely carry out cleaning methods
- Solve problems within their responsibility and others under their control
- Leave the work area clean and tidy
- Lead by example when supervising others and work effectively
- Understand and carry out pre- and post-clean testing and reporting
HEALTH & SAFETY
Kitchen extract duct cleaning is a necessary safety measure in most jurisdictions around the world. The EU provides overarching Directives which are adopted into more detailed national law. Specialist cleaners will follow at least the minimum requirements of national law, and the standards and good practice which will help them to achieve the targets of the law.
There is no one-size-fits-all answer for how to reduce the risk of accidents in the workplace. The best way to protect employees depends on the hazard itself. Some common ways to reduce risk are to:
- Avoid the hazard completely by carrying out the work differently, e.g. avoid Restricted Access or Confined Space entry to ductwork by using remote-working machines and tools
- Design a safe method of work
- Train operatives
- Provide tools and equipment suitable to the job, and which are safe to use
- Control the exposure to the hazard
- Supervise work
