REDUCING FUME EXPOSURE
How to reduce exposure to fumes during thermal cutting
You cannot make an omelet without cracking eggs – or release harmful gases and fumes. Depending on the base material and the gas used, plasma, laser, or oxyfuel cutting processes release extremely fine particles of zinc, lead, cadmium, chromium, beryllium, and other constituents into the environment. Some of these are highly harmful to health and can cause serious illnesses in humans. This makes it all the more important to avoid inhaling any released fumes when cutting sheet metal. There are various precautionary measures and solutions for this, which we would like to outline here
Parameters influencing fume gas development
The composition and intensity of the cutting fumes depend on various parameters:
- Material composition of the material to be cut
- Cutting method (plasma, laser, or oxyfuel cutting)
- Sheet thickness or material thickness
- Fuel gas used (plasma gas, nitrogen, compressed air)
- Cutting gas pressure
- Cutting speed and cutting length
Looking more closely at the parameters, the composition of the base material plays the most important role. Its components primarily determine the chemical composition of the particles released during cutting.
During thermal cutting, the particles of these dusts are somewhat larger than those produced during thermal joining (welding), but they are still fine enough to enter the human lungs. This makes them hazardous to health and, depending on their components, can even cause cancer. During laser cutting, the released particles are even smaller or finer than during plasma or oxyfuel cutting due to the high energy density of this process and can penetrate cell walls.
Source: European Welding Association (EWA), Technical Committee „Health and safety equipment“ (TC HSE), information paper, draft as per 03/2024 „Introduction in methods of prevention and extraction of welding fume“
In addition to the fine dust, so-called nitrous gases such as nitrogen oxide are produced. These are respiratory poisons with irritating and corrosive effects and can cause lung damage (pulmonary edema) even 24 hours after inhalation.
Each of the cutting processes is complex and poses its own unique hazards, which we won’t discuss in detail in this article. Instead, we want to focus on solutions for reducing exposure to cutting fumes. Well, how to reduce exposure to fumes during thermal cutting?
Fact check on site
If you only cut components occasionally, you’ll work under different conditions than if you work shifts processing tons of sheet metal. Even though you often read that natural ventilation, such as regularly opening the shop door, is sufficient for occasional thermal cutting, you must ensure you have adequate PPE (personal protective equipment). This includes, at a minimum, a ventilated helmet.
If thermal cutting is your regular daily activity, you definitely need a well-designed industrial air cleaning system that fits your needs. There are many customized solutions available. In that article, we would like to introduce to you some of them.
Reducing cutting fumes through the process
Similar to welding, you can adjust the parameters for cutting to reduce emissions from the cutting process. For example, using a 2.4 mm cutting nozzle and 150 amps allows you to work quickly. However, this creates more emissions than cutting with a 1 mm cutting nozzle and 80 amps. The joint is narrower, and the emissions are lower.
Affection of process gases
Process gases also affect the formation of fumes and dust during cutting. Laser cutting produces the least amount of process gas. This cutting process is primarily used for thin sheets less than 10 mm thickness. However, there are now also cutting lasers that can cut sheets with up to 60 mm thickness. Due to the radiation, laser cutting must always be carried out safely and isolated from the surrounding environment by a closed housing. It must be 100 percent impossible for reflections to unintentionally deflect the laser beams. A laser cutting head attached to a robot is only permitted in an enclosed space that cannot be entered during the activity.
Plasma cutting often requires two process gases: the plasma gas, which transfers electrical energy to the workpiece and melts the material. The second is the so-called shield gas, which acts as a process gas to blow out the melted material. If compressed air is used as the shield gas, harmful gases are also produced: nitrogen monoxide and nitrogen dioxide. These are also called NOx, i.e., gaseous compounds of nitrogen and oxygen. By using pure nitrogen as shield gas, you can prevent the formation of harmful NOx because the plasma gas does not contain oxygen as a reactant.
You can also use argon or argon-hydrogen, for example, to reduce emissions. It’s important that the nitrogen doesn’t have oxygen available as a reactant.
Oxyfuel cutting – also known as autogenous cutting – is primarily used for cutting structural steel, especially unalloyed and low-alloy steels. Acetylene, propane as well as propane-butane are used as the fuel gas. Acetylene has a narcotic effect on humans if inhaled.
Emissions can never be completely eliminated, so fume extraction during cutting is the best way to protect employee health. When cutting sheet metal in the workshop, cutting tables with the possibility to extract fumes and water tables offer the best protection. Both options are also highly efficient.
Cutting tables with integrated extraction
The closer the extraction system is to the process, the more emissions can be directly captured. In thermal joining (welding), this is referred to as extraction at the source, where a special extraction torch directly captures the resulting, upward-rising fumes. During thermal cutting, the emissions are almost exclusively blown downwards, i.e., beneath the workpiece. Gases only escape upward during ignition or when piercing the cut. For this reason, extracting the cutting fumes via the cutting table is recommended.
Cutting table principle with integrated extraction
Picture: Downdraft cutting table, front and side view
Cutting tables with integrated extraction systems (downdraft table) are usually quite large. To ensure the most efficient extraction, the cutting tables are further divided into segments (image right, side view). Using a button, for example, the cutting torch activates the opening of the extraction area directly below. This allows for more efficient extraction at specific points, as extraction is only active in the segment over which the cutting torch is currently positioned.
The slag produced during thermal cutting drops into the slag container. Sparks drawn in cool on the side metal sheets and fall down as well. The gaseous emissions are channeled into the extraction duct (see front view, left image) and conveyed through a pipeline to the filter system.
Recommendation for downdraft cutting table
HERR® extraction table PorVent – energy efficient, easy installation and maintenance
Details: https://ex-track.com/herr-downdraft-table-1600×3200/
Picture: HERR® downdraft table 1600 x 3200
Principle cutting table as water table
Picture: Cutting water table
With a water cutting table, the jet that shoots downward during cutting is trapped in a water bed. Slag and coarse particles naturally drop into the water basin. A water cutting table is filled with water to approximately 20 mm below the bottom edge of the workpiece. Naturally, a small amount of flue gas can also escape through the small gap between the cutting grid and the water surface.
The efficiency of an extraction table with dry extraction is higher than that of a water cutting table. If small sheets of metal need to be cut, the efficiency of the extraction table can be increased even further by covering the cutting grid with additional sheets. A water cutting table does not require an additional filtration system, but the water must be continuously “treated” with chemical additives, and the contaminated water must be repeatedly disposed of. Depending on the size of the table, an additional 800 to 1,000 liters of water are added as a weight component, which must be considered when selecting a location. Depending on the on-site conditions, a water extraction table is a simple solution.
Recommendations for water cutting tables
HERR® water extraction table 1,600 x 3,200 mm of the CT-PORW series – solution for portable cutting systems, ideally suited for EX-TRACK® CNC cutting system
Details: https://ex-track.com/herr-water-table-1600-3200/EX-TRACK® water table 1,000 x 2,000 mm – small and highly efficient, especially for EX-TRACK® CNC cutting system
Details: https://ex-track.com/ex-track-water-table/
Picture: EX-TRACK® water table 1000 x 2000
Small working tables
Picture: Working tables
The operating principle of a manual cutting table is similar to that of a large cutting table with extraction. However, due to the small cutting surface, the table is no longer divided into individual sections. The material is placed on the cutting grid and cut. Any sparks and slag that are created fall directly onto the cutting grid and are collected, preventing them from being sucked into the extraction system. The light gaseous particles are captured by the slots in the extraction pipe and from there transported via the pipe system to the filter system.
Recommendation for small manual working tables:
HERR® working table – for cutting and welding
Details: https://ex-track.com/herr-hand-plasma-cutting-and-welding-table/
The filter system
The particles and fumes emitted from the cutting table are directed to the extraction filter system (see illustration on the left) and captured in the filters. The air inlet can also be opened downwards if required. Baffle plates are installed directly behind the inlet. These prevent sparks or larger particles from damaging the filters. Such larger particles directly drop into the collection box and are captured there.
Picture: Filtration system – The right image shows a cross-section through the filter and its flow path.
Depending on local regulations, the purified air is either discharged directly into the environment or vented outside via the existing exhaust system. The most commonly used filter systems for cutting are low-vacuum systems. These offer a high volume flow at low static pressure.
Is a filter efficiency of 99.99 % sufficient for particle sizes ≥ 0.5 µm?
The direct answer to this question is: no. Reason: 98.90 % of all particles are < 0.4 µm in size. This means that a maximum of 1.1 % of the total particle volume is captured in the “coarse” filter. For a particle size of ≥ 0.5 µm, only < 10 % of all particles can be captured with a filter efficiency of 99.99 %.
Our tip: Filter cartridges certified according to DIN 1822 / ISO 29463
Make sure your filter system also captures particles smaller than 0.4 µm. Filter cartridges certified according to DIN 1822 / ISO 29463 meet the requirements for this particle size. These filters are often also referred to as filter for suspended particles. Filters of this type must then meet at least filter class E10. HERR® filter systems comply with filter class E11.
Recommendation for efficient filter systems:
880 series from HERR® with 2 filters à 20 m2 filter surface – very compact, lightweight and highly efficient extraction system, suitable for PorVent cutting table
Details: https://ex-track.com/central-extraction-system/
Final recommendations
- The fumes produced during cutting are harmful to health and must be prevented from entering the human respiratory tract. Cutting tables with integrated extraction offer the most efficient solution.
- Whether a cutting table with dry extraction and a connected filter system or a water table is chosen depends on local conditions and individual preferences.
- The most important thing is that the emissions do not pose a toxic load to people or the environment.
We hope the article was useful for you. We also recommend another article related to the theme, How To Eliminate Air Pollution During The Cutting Process. If you needed any further help, please do not hesitate to contact us at the following email: support@thermacut.cz
Text: Thermacut, k. s.,
Photo: archive of Thermacut, k. s.