Some of the most Frequently Asked Questions put to us regarding extraction – or Local Exhaust Ventilation as it’s officially termed. Click on a question below to get an answer.
What is an LEV system?
LEV stands for Local Exhaust Ventilation and is an engineering control system designed to control airborne contaminants such as fumes, mists, dusts, vapours or gases in the workplace
An LEV system is more commonly referred to as an extract system. But this is a very broad description that can cover a wide range of products and solutions. From simple recirculating, under the bench units – to site-wide, centralised extraction systems.
Harmful, airborne contaminates have a proven history of causing a range of health issues from occupational asthma to lung disease, cancer and even death. You are legally required to protect employees against them. Many workplaces and industries will have a need for controlling substances hazardous to health and will have to meet certain COSHH Requirements to do this. An LEV system is part of this and falls under Regulation 7 of COSHH.
LEV systems are specifically designed to protect employees from harmful, airborne contaminants in the workplace.
Most LEV systems (but not all) comprise of:
- Capture Device: This is where the contaminant “cloud” enters the LEV
- Ducting: This can be simple flexible ducting or more complex steel ducting. Ducts conduct the contaminated air from the hood to the filters and/ or discharge point
- Air Cleaner or Filter: These clean or filter the contaminants out of the air stream before discharging the air
- Air Mover: More commonly referred to as a Fan. These power the system
- Exhaust or Discharge: This releases – or “vents” the extracted air into a safe place
How do I know if I need to install an LEV system?
An LEV system is often a “last resort” and there are several other factors that need to be considered before looking at an LEV System.
The HSE have a range of guide publications which will help you understand if you need an LEV System. These publications cover both general LEV systems and more indepth ones for specific industries like woodworking or welding. These can be downloaded for free from the HSE website.
LEV systems are also limited to what they are designed to do. For example a process maybe to large for an LEV system to control on its own and needs to work alongside other controls.
Before deciding to look at LEV systems you need to consider:
- Can you eliminate the source completely? – this is usually impossible or not practical
- Can you substitute the material being used for something safer?
- Can you reduce the size of the source/ amount of substance being used?
- Can you modify the process to reduce the exposure risk or amount of particulates emitted?
- Can you reduce the number of employees involved with the process?
- Can you apply other simple controls such as lids or close off sections of the process?
- Will any of the above help reduce the scale or scope of an LEV system if implemented along side?
If you can not mitigate or control the exposure by other means where reasonably practical then an LEV system needs to be considered.
Can I filter fume and dust?
Two types of filters are used to remove most fumes (including Vapours and Gases) and dusts (including fibers and shavings). These are Particulate Filters for dusts and Carbon Filters (sometimes called Gas Filters) for Fumes.
Some times a process will need to be vented to atmosphere as filters may not be effective enough or commercially viable. However, each system needs to be designed individually based on the contaminate being created, the process creating it, the operators activities and budgets
All particulate filters are graded and designed for different types and sizes of dusts. Course dusts like wood shavings or GRP dust only need quite low efficiency filters. Where as fine dusts such as carbon fibers, chemical powders will need the highest grade filters.
Having the right filter is vital to a system’s effectiveness. If a high grade filter is used on a course dust it will quickly block up and need replacing frequently, pushing up running costs. Equally a fine dust through a low efficiency filter is ineffective as the filter could be to course to stop the dust from escaping
The same is true for carbon filters. There are different grades of carbon filters for different vapours – such as carbon filters treated for acid fumes or formaldehyde vapours. Using the wrong carbon filters can result in ineffective filtration or even unknown and adverse chemical reactions
For abit more of an indepth look at fume and dust extraction you can look at our respective dust or fume extraction pages and our Filtered Extraction Page. Click the links below.
What is HEPA filter?
HEPA stands for High-Efficiency Particulate Air. HEPA filters are very fine filters and some of the most efficient particulate filters generally available on the market today. HEPA Filters are usually made of many layers of interwoven fibreglass strands.
HEPA filters are mostly classed as being able to filter out 99.997% of contaminants in the air stream that are 0.3 microns or bigger.
To put that into perspective a human hair is around 100 microns and the naked eye can’t see much smaller than around 30 microns.
So a HEPA filter can remove dust particles that are 100 times smaller than you can see.
What is a carbon filter?
A Carbon filter is designed to remove gases and vapours from air streams. It is full of tiny pieces of carbon – which are normally referred to as Activated Carbon. More often than not, this is made from coconut husks.
Activated Carbon has a massive surface area. One gram of Activated Carbon has a surface area in excess of 3,000 square meters (as determined by Gas adsorption).
Activated Carbon works by allowing the contaminated air to pass through it. Any chemical vapours and gases in the air stream are attracted to the carbon surface and bonded via a process called Van der Waals Force (a distant-dependent interaction described in molecular physics).
Carbon Filters can be further treated with other elements to make them effective in filtering different chemicals like Acids or Formaldehyde.
Common attributes of Carbon Filters are:
- Will Adsorb almost any vapour – with the right treatment.
- Have a large capacity for Organic Solvents.
- Can absorb different chemicals at the same time.
- Is highly effective at removing Ozone – one of the principal components of smog.
- Is inert and safe to use.
The amount of carbon in the filter matters. As the filter is dependent on the contaminated bonding to the carbon as they pass by, the amount of time they have to do this is vital. This is referred to as the dwell time.
By having more dwell time, the filter can be more effective and will last longer.
How long do filters typically last?
This is a very difficult question to answer and one we get asked a lot. There are a lot of variables to consider when trying to work out filter life expectancy. These can include:
- Type of filter – Particulate or Gas, bag filter or panel filter, fine dust filter or course filter etc.
- Type of contaminate being extracted.
- The process that generates the contaminate.
- The amount of contaminate being generated and extracted.
The amount of particulate being generated is the main factor in how long a filter lasts. The more contaminate that is generated the faster the filter will saturate (fill up).
We try and specify filters big enough to handle the amount of contaminate generated for a sensible amount of time – around 8 – 12 months.
As a rule of thumb, if the filters are the correct type, grade and size and the LEV system is specified, designed and installed properly, then filters should last as follows:
- Pre-Filters: 1 – 3 Months.
- Main HEPA and/ or Gas filters: 8 – 12 Months.
There are ways to increase filter life by using things like in line “slave” filters such as pre-separators, cyclone filters etc. But these should only be used if allowed for in the system design and performance.
There are also cleanable dust filters. These are designed to last years and can be cleaned within the confines of the LEV system, usually with an air pulse jet system or a vibration system.
Please be aware: Disposable filters CAN NOT be cleaned and must NEVER be washed. To try and do so could pose a serious health risk to those involved. A saturated disposable filter MUST be disposed of safely and replaced.
Does my LEV system need to be checked?
Yes. Under COSHH Regulation 9 you have to periodically check your control measures to ensure they are still effective at protecting your workers. Each control measure will have its own guidelines on how often this needs to be done.
An LEV system needs to have a Thorough Examination and Test at least every 14 months. This should be carried out by a competent and trained person.
An LEV system also must all have routine low-level inspections to ensure the system is still operational, effective and free of damage. These should be carried out weekly and recorded in a system logbook. These should be kept for as long as the life of the system
Under Health and Safety and COSHH, you are legally required to prove your hazard control measures are not only effective but also checked to ensure they remain effective throughout the lifetime of the control
Vodex Extraction Services
Vodex Ltd has over 30yrs experience in handling fume extraction and we offer a whole range of extraction products for fumes and vapours. We have worked in a very wide range of applications. As always if you need any further information, have any questions or just want to chat about your application or requirements then please feel free to contact us. Its really easy to do.
You can email us at sales@vodex.co.uk, use our website contact form, use our online, secure web chat or call us on 01489 899070.
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