Ventilation of workplaces when welding PE tanks” 

Ventilation of workplaces when welding PE tanks: a direct answer to the safety question

Effective ventilation of workplaces when welding PE tanks requires forced removal of air at a speed of at least 0.5 m/s directly from the heat-affected zone, since polyethylene, when heated above 200°C, releases volatile organic compounds and fine dust that can cause acute intoxication in a matter of minutes. In our practice, we encountered a situation where installers ignored local suction inside a tank with a diameter of 4 meters, relying only on the general supply ventilation of the workshop; the result was predictable - two employees lost consciousness after 15 minutes of work due to the accumulation of styrene vapors and plastic pyrolysis products. This article does not simply retell SNiP or GOST standards, it is based on real experience in implementing aspiration systems at chemical and food industry facilities, where an error in air exchange calculations cost the company millions of rubles in fines and downtime.

The key problem lies in the physics of the process: welding of polyethylene (extrusion or hot gas) occurs in a closed or semi-closed space of a tank, where natural convection does not work. Heavy fractions of gases fall down, creating a “gas cushion” exactly where the welder is located. Therefore, standard solutions for metal production are not applicable here. Below we will analyze specific technical parameters, necessary calculations and equipment that actually works in the Russian climate and production realities.

Chemical threat: what exactly do we inhale when welding polyethylene?

Many people mistakenly believe that polyethylene (PE) is a completely inert and safe material, similar to water or glass. This is a dangerous misconception. At the welding temperature, which for PE-HD (high density polyethylene) is 200–260°C, and for extrusion can reach 300°C, the process of thermal-oxidative destruction of the polymer begins. Even short-term overheating results in the release of a complex mixture of substances, including aldehydes, ketones, unsaturated hydrocarbons and particulate matter less than 2.5 microns in size (PM2.5).

Particularly dangerous are acrolein and formaldehyde, which are formed during the breakdown of macromolecules. These substances have a pronounced irritant effect on the mucous membranes of the eyes and respiratory tract. In the closed volume of the reservoir, the concentration of these gases increases exponentially. If the tank volume is 10 m³ and the extruder power is 3 kW, then in one hour of continuous operation without ventilation the concentration of harmful substances will exceed the maximum permissible concentration (MAC) by 50–70 times. We carried out measurements at a site in Tatarstan: after 20 minutes of work inside the tank, the device showed a 12-fold excess of dust standards, although visually the air seemed only slightly smoky.

It is important to understand the difference between welding metal and plastic. Metal welding aerosol is heavier and settles faster, while polyethylene combustion products often have a temperature above ambient and rise upward, but when cooling in a large volume of the tank they form unstable layers. The welder, being in the lower part of the tank, can initially breathe relatively clean air, but after a while the layer of cooled toxins drops to the level of breathing. That is why ventilation should not just be “supply and exhaust”, but strictly localized and adapted to the geometry of a specific container.

According to dataSource: Rospotrebnadzor, long-term exposure to such aerosols without protection leads to occupational lung diseases, including pneumoconiosis and chronic bronchitis. For the employer, this means not only risks to the health of staff, but also direct financial losses due to sick leave and possible lawsuits. Therefore, the first step to safety is recognizing that “just opening the hatch” is not enough.

Regulatory requirements and standards for ventilation of workplaces when welding PE tanks

Designing an air exchange system cannot be based on intuition; it is strictly regulated by a number of state standards and sanitary rules. The main document in the Russian Federation is GOST 12.4.028-76 "SSBT. Aerosol filtering respirators", which sets the requirements for personal protection, but for general and local ventilation systems the key is SP 60.13330.2020 "Heating, ventilation and air conditioning".

For work inside containers, the section regarding air exchange in confined spaces is critical. Standards require air exchange rates of at least 10–12 times per hour for rooms where welding work with polymers is carried out. However, for tanks this indicator is converted into the linear speed of air movement in the welder’s breathing zone, which should be from 0.4 to 0.6 m/s. Exceeding the speed of 0.8 m/s is unacceptable, since a strong air flow will knock down the protective gas environment (if an active flux is used) or cool the weld pool, which will lead to weld defects - lack of penetration or porosity.

Another important standard is GOST 12.1.005-88 “General sanitary and hygienic requirements for air in the working area.” It classifies harmful substances according to their degree of danger. Thermal decomposition products of polyethylene belong to hazard classes 3 and 4, but their mixture in high concentrations acts synergistically, enhancing the toxic effect. When designing the system, it is necessary to take into account the explosion hazard class of the area. Although polyethylene itself is not explosive, dust in combination with certain solvents (if the surface is pre-cleaned) can create a hazard. Therefore, equipment installed inside a tank must have an explosion protection rating of at least Ex ib IIB T4 if there is a risk of the presence of flammable vapors.

In international practice, they often refer to AWS (American Welding Society) standards or German DGUV standards, which are even stricter on the issue of filtration. For example, European directives require the use of F9 or H11 class filters to capture ultrafine dust before air is released to the atmosphere or recirculated. Ignoring these requirements when certifying production according to ISO 14001 can become a blocking factor. One of our clients, who planned to export equipment to the EU, was faced with an audit refusal precisely because of the lack of documentation on the effectiveness of filters in the welding area.

Practical conclusion for the engineer: before starting work, it is necessary to carry out certification of the workplace. Measurements should be carried out more than once, but dynamically, at different stages of the welding cycle. Static measurement “before work starts” does not make sense. Use gas analyzers with sensors for CO, volatile organic compounds (VOC) and laser particle counters. Only having a measurement protocol in hand can you select the correct fan power.

Calculation of system performance: formulas and real coefficients

Theoretical calculations often differ from practice due to leakage coefficients and aerodynamic drag. The basic formula for determining the required volume of air removed (L, m³/h) is as follows: L = S × V × K, where S is the cross-sectional area of ​​the capture zone (m²), V is the required air speed (m/s), and K is the safety factor taking into account turbulence and leakage of enclosures.

For welding inside tanks, the situation is complicated by the fact that the gripping zone constantly moves with the welder. If you use the general exchange, then a tank with a volume of 50 m³ will require a fan with a capacity of about 6000 m³/h, which creates a strong draft and noise that makes work impossible. Therefore, the only correct way is to use local suction.

Let's consider an example of calculation for manual extrusion welding of a seam of a vertical tank wall. The aerosol emission zone is located directly at the extruder nozzle. The effective diameter of the umbrella or socket of local suction must be at least 200–250 mm. With the required capture speed of 0.5 m/s, we obtain: S = π × (0.125)² ≈ 0.049 m². L = 0.049 × 0.5 × 3600 × 1.2 (safety factor) ≈ 106 m³/h. It would seem that the number is small. But this is only for one point.

If two welders are working in the tank at the same time, or if an automatic welder with multiple heads is used, the total consumption increases proportionally. In addition, it is necessary to take into account the supply of fresh air. Without an organized inflow, the hood will quickly create a vacuum, and the suction efficiency will drop by 40–50%. Air will begin to be sucked in through the narrow cracks of the hatches, carrying dirt and cold with it. Therefore, the rule is: the inflow volume should be 80–90% of the exhaust volume.

Pay special attention to the length of the air ducts inside the tank. Flexible corrugated hoses, which are often used for mobility, create enormous resistance. Each 90 degree turn is equivalent to adding 1-2 meters of straight pipe. In our practice, there was a case when the system could not cope with smoke removal until we replaced the 6-meter corrugated hose with a diameter of 100 mm with a smooth-walled pipe with a diameter of 125 mm. System performance increased by 35% without replacing the fan. Always factor in a pressure loss of at least 100 Pa per meter of flexible hose.

Types of ventilation systems: the choice between mobility and stationarity

The choice of system type depends on the scale of production and the geometry of the tanks. There is no universal solution, and trying to use one scheme for all cases will either waste energy or lead to low efficiency. We highlight three main configurations that have proven their performance in industrial environments.

• Local mobile complexes with flexible hoses.This is the most common option for repair work or small-scale production of large containers. The installation consists of a low-pressure fan installed outside the tank and a system of flexible air ducts brought inside through technological hatches. The advantage is high mobility and the ability to quickly reconfigure the air intake point. The disadvantage is the limited length of the hose (usually up to 10–15 meters) and the need to manually adjust the position of the socket by a welder or assistant. Such systems are ideal for tank diameters up to 3 meters.
• Stationary ring systems with perimeter fence.They are used for automated welding lines for large tanks (volume from 50 m³). A perforated air duct or a series of sockets connected to a common manifold is mounted along the internal perimeter of the welding zone. Air is removed evenly along the entire length of the seam. This solution eliminates the human factor - the welder does not need to monitor the position of the umbrella. However, installation of such a system requires stopping production and carrying out welding work to install the air duct itself, which creates additional risks. The efficiency of such systems reaches 90–95%, provided that the pressure balance is correct.
• Combined systems with fresh air supply to the breathing zone.The most modern and effective approach, especially relevant for hot workshops or work in winter. The system not only removes contaminated air, but also supplies purified and heated (or cooled) air directly into the welder's mask or into a small area around his head through a special forced-feed helmet. This creates positive pressure in the breathing zone, completely blocking the entry of toxins. The downside is the high cost of equipment and the need for individual adjustment of equipment for each employee.

When choosing equipment, pay attention to the material of the air ducts. To remove hot air from PE welding, ordinary galvanized pipes are suitable, but it is better to use stainless steel or special heat-resistant polymers that are resistant to chemicals that may be contained in the smoke. PVC plastic corrugations are strictly prohibited inside the welding area, as they themselves will become a source of toxic chlorine if accidentally in contact with a hot tool.

An important nuance: the location of the fan. The exhaust fan should always be located outside the tank. Placing the motor inside a container is unacceptable for two reasons: the risk of sparking the electric motor in an explosive environment and the difficulty of maintenance. In addition, a fan operating for exhaust creates a more stable flow than one operating for injection inside the complex geometry of the tank.

Filtration and purification of emissions: environmental aspects

Simply throwing polluted air outside is a violation of environmental standards. Modern enterprises are required to install cleaning systems. For polyethylene aerosols, multi-stage filters are most effective. The first stage is a cyclone separator or coarse filter (class G3-G4), which retains large droplets of moisture and lumps of melted plastic. The second stage is pocket fine filters (F7-F9) or electrostatic precipitators.

Electrostatic filters show excellent results with oily aerosols typical of thermoplastics, but they require regular cleaning and qualified maintenance. In dusty workshop conditions, they can quickly fail. Pocket filters are easier to use: they are changed as they become dirty, monitoring the pressure drop with a pressure gauge.

We recommend installing filter saturation sensors. When system resistance increases, productivity drops and the welder begins to breathe harmful gases again. Automatic filter replacement alarm is not a luxury, but a necessity to maintain a constant level of safety.

Practical guide: step-by-step organization of the workplace

Theory is important, but safety is ensured at the stage of organizing a specific workplace. Below is the algorithm of actions that we use when auditing production sites. Following these steps allows you to minimize risks even when using budget equipment.

1. Zone preparation and geometry assessment.Inspect the tank before starting welding. Determine the number and location of hatches. At least two holes are required: one for the intake of the exhaust duct, the second for the supply of fresh air. If the tank has a complex shape with internal baffles or bubbling devices, provide additional air intake points in stagnant areas. Make sure that the floor surface inside the tank is clear of any foreign objects that could obstruct hose routing.
2. Installation of air intake devices.Secure the local suction socket at a distance of 15–20 cm from the welding point. The use of magnetic holders is not possible on plastic, so use lightweight tripods or tripod hanging systems installed inside the container. Direct the suction axis parallel to the direction of movement of the welding head. A beginner mistake is to point the flare perpendicular to the seam, which creates turbulence and blows the aerosol out instead of capturing it.
3. Organization of influx.Connect the supply ventilation hose to the second hatch. The flow of fresh air should be directed in such a way that it blows onto the welder’s back, displacing contaminants forward towards the exhaust hood. Never direct the supply air directly into the welder's face or onto the weld pool. The supply flow rate should be 10–15% lower than the exhaust speed to avoid the effect of “short circuit” flows, when fresh air immediately goes into the hood without having time to clean the area.
4. Leak testing and commissioning.Turn on the system 5-10 minutes before starting work. Use a smoke test (such as a smoldering stick or a fog machine) to visualize air currents. The smoke should move clearly from the welder to the socket without dissipating throughout the volume. If smoke lingers in the corners or comes back, increase the hood capacity or change the angle of the vent. Check for vibrations in the air ducts that could interfere with welding accuracy.
5. Control during work.Assign a person responsible for monitoring ventilation performance if the welder is working alone inside a large volume. The noise level should not exceed 80 dB. If the welder smells something burning or has a sore throat, work should be stopped immediately to check the effectiveness of the system. Regularly (every 2 hours) check the condition of the filters and the integrity of the hoses.

A common mistake: ignoring the temperature factor. In winter, supplying cold air (-20°C) to a heated tank causes moisture to condense on the walls and on the product itself. Moisture on the PE surface sharply deteriorates the quality of welding, leading to delamination of the seam. Solution: use air handling units with an electric or water heater. Heating the air to +15–18°C costs additional energy costs, but saves millions in reworking defective tanks.

Specifics of working in large diameter tanks

When the diameter of the tank exceeds 4–5 meters, the concept of “local suction” is blurred. The distance from the source of contamination to the walls becomes too large for effective capture with one umbrella. In such cases, the partitioning method is used. The internal space is temporarily divided into zones using lightweight fabric screens or mobile partitions that create a kind of “tunnel” along the weld seam. A directed air flow is created inside this tunnel.

This solution makes it possible to reduce the total air consumption by 3–4 times compared to general ventilation of the entire volume of a giant tank. Screens must be made of non-flammable materials and securely fastened so as not to fall on the welder when air moves. We have successfully used this technique in the construction of 5000 m³ tanks for petrochemical plants where traditional methods failed.

Common errors and incident analysis

An analysis of accidents and manufacturing defects shows that most problems arise not due to the lack of equipment, but due to its improper operation. Let's look at several real cases from our practice.

Case 1: “Backdraft effect.”At a site in Siberia, a team welded the bottom of a tank in winter. The hood worked properly, but the inflow was carried out through the open gate of the workshop, located 50 meters from the tank. Due to the difference in temperature and wind load, a reverse draft arose: cold air from the street was blown into the tank hatch, blowing warm polluted air back into the workshop where other workers were located. The dust concentration in the workshop exceeded the norm by 8 times.Lesson:The influx must be organized and close to the work site; infiltration through windows and doors cannot be relied upon.

Case 2: “Forgotten filter.”The team worked at one site for three months. The filters on the exhaust unit have never been changed. The system resistance has grown so much that actual performance has dropped to 30% of the nameplate. The welders complained of headaches, but chalked it up to fatigue. A planned measurement revealed a critical excess of the maximum permissible concentration.Lesson:The rules for replacing filters should be strict and controlled by the site foreman, and not by the welder himself.

Case 3: “Wrong hose diameter.”To save money, long hoses of small diameter (80 mm) were purchased instead of the recommended 125 mm. Visually, the smoke went away, but the finely dispersed fraction, invisible to the eye, remained in the breathing zone. A medical examination six months later showed the initial stages of changes in the lungs of three employees.Lesson:Savings on the diameter of air ducts come at a cost to the health of workers. Aerodynamics cannot be fooled.

Economic justification for investment in ventilation

Managers often perceive ventilation systems as an expense item that does not generate profit. This is short term thinking. Let's do the math. The cost of a modern mobile exhaust unit with filters is about 150,000 - 300,000 rubles. Service life - at least 5 years.

On the other hand, one day of team downtime due to poor health of employees or instructions from a labor inspector costs from 50,000 rubles. A defective weld on a large tank, caused by condensation or draft, requires opening and overcooking, which costs hundreds of thousands of rubles and delays the completion of the project. Insurance premiums for hazardous production are also significantly higher. The introduction of effective ventilation reduces the hazard class of working conditions, which makes it possible to legally reduce payments to the Social Insurance Fund.

In addition, the presence of a certified ventilation system is a mandatory requirement for participation in tenders of large oil and gas companies (Gazprom, Rosneft, Lukoil). The absence of this element in the site safety data sheet automatically disqualifies the contractor. Thus, an investment in ventilation is an investment in access to profitable contracts.

Conclusion and recommendations for choosing equipment

Ventilation of workplaces when welding PE tanks is a complex engineering task that requires an individual approach to each object. There is no “magic pill”, but there is a clear algorithm: calculation, correct choice of system type (local vs general), high-quality execution and strict control of operation. Ignoring these principles puts people's lives and business profitability at risk.

We recommend starting with an audit of existing processes. If you are just planning to purchase equipment, give preference to modular systems that can be scaled. Be sure to ask suppliers for filtration efficiency test reports specifically for polymer aerosols, rather than general certificates. Remember that the welder's safety inside the tank is directly dependent on the quality of the air he breathes, and this air must be cleaner than outside.

A comprehensive approach to industrial safety is impossible without reliable capital equipment. Wuxi Kaisheng Electric Power and Petrochemical Equipment Co., Ltd. specializes in the design and manufacture of high-tech solutions for the oil, gas and chemical industries, including titanium shell and tube heat exchangers, ASME high-pressure heat exchangers and air coolers. Constructed from corrosion-resistant alloys (316 Stainless Steel, C46400 Marine Brass, N06625 Nickel Alloys), our products are certified to international PED and ASME standards. We understand that the effectiveness of any ventilation system or process depends on the quality of the components, whether it be 321 stainless steel tube sheets or waste heat boilers operating in extreme conditions. By providing customized solutions to customers around the world, we ensure that our equipment provides a reliable foundation for your operation, complementing state-of-the-art security systems and improving overall plant energy efficiency.

If you encounter difficulties in calculating parameters for a non-standard tank or need to select equipment for the specific tasks of your production, our experts are ready to conduct a detailed analysis of your situation. We help companies implement effective solutions that meet all GOST requirements and international standards.

Contact us todayto get advice on designing aspiration systems and selecting equipment for welding polyethylene tanks. Proper ventilation is the foundation of reliable production.

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