MERV Ratings: Choosing the Right Filter for Welding Fume Extraction

Welding, a vital process in many industries, releases harmful fumes and particulates that pose significant health risks. Effective fume extraction is essential for worker safety and compliance with health standards. At the core of this extraction process is the choice of the right filter, guided by MERV (Minimum Efficiency Reporting Value) ratings.

These ratings determine the filter’s effectiveness. This article delves into understanding MERV ratings and their importance in selecting the appropriate filter for welding fume extraction, aiming to provide essential insights for a safer, healthier workplace.

For welding fume filtration, MERV-13 is typically the minimum recommended, effective for particles ranging from 0.3 to 1 micrometer. However, consider MERV-16 or higher to ensure a safer breathing environment for capturing carcinogenic pollutants or manganese.

Welding fumes need to be filtered if they are recirculated back into the working environment. When welding fumes are exhausted outside, it’s crucial to adhere to company environmental standards, such as ISO 14001, along with local and federal environmental regulations. This will determine whether the fumes must be filtered before being released into the environment.

What are MERV Ratings?

MERV stands for Minimum Efficiency Reporting Value, a rating system that classifies air filters based on their ability to capture airborne particles of different sizes. The MERV rating system is a critical factor in selecting the appropriate air filter for welding fume extraction, as it directly impacts the quality of air that workers breathe in the vicinity of welding operations.

MERV Rating	0.3 to 1 Micron	1 to 3 Microns	3 to 10 Microns
1-4	<20%	<20%	<20%
5	<20%	<20%	20 – 34%
6	<20%	<20%	35 – 49%
7	<20%	<20%	50 – 69%
8	<20%	<20%	70 – 85%
9	<20%	>50%	≥85%
10	<20%	50 – 64%	≥85%
11	<20%	65 – 79%	≥85%
12	<20%	80 – 89%	≥90%
13	>75%	≥90%	≥90%
14	75 – 84%	≥90%	≥90%
15	85 – 94%	≥95%	≥90%
16	≥95%	≥95%	≥90%
17-20 (HEPA)	>99.97%	≥99%	≥99%

MERV ratings serve as a guide to determining how effectively a filter can remove particles of varying sizes from the air. As these ratings increase, so does the filter’s ability to capture smaller particles. When it comes to welding fume extraction, understanding the specifics of MERV ratings is essential for selecting a filter that balances efficiency with practical needs in the workplace. The selection process should consider the nature of the welding work and the type of particulates present to ensure adequate protection and air quality.

Recommended MERV Ratings for General Welding Applications

Scientific research has shed light on the particle size range and distribution in welding fumes, which is critical for selecting the appropriate MERV rating for filtration.

Welding fumes consist of fine particles and gases capable of penetrating deep into the lungs. Particle size in welding fumes varies from 0.005 to 20 micrometers (µm), with a significant portion of these particles being smaller than 1 µm. In particular, gas metal arc welding (GMAW) produces fume particles that are predominantly smaller than one micrometer​.

Given this particle size distribution, it’s evident that welding fume extraction requires filters capable of efficiently capturing ultrafine particles. A filter with a MERV rating that effectively captures particles between 0.3 to 1 µm and 1 to 3 µm is recommended for general welding applications. This would ensure that most welding fume particulates, known to be hazardous to health, are adequately filtered out.

Therefore, a MERV rating of at least 13 is advisable for general welding applications, as it ensures high efficiency in capturing particles larger than 0.3 µm (greater than 75% efficiency) and provides the best balance between filtration efficiency and airflow resistance. Filters with MERV ratings of 14 or higher offer even greater efficiency and are suitable for environments where the highest level of air purity is required.

Considering the diversity of welding fumes, which vary based on the welding process, materials used, and other parameters, there is no one-size-fits-all filter solution. Each welding operation can generate a unique set of pollutants and particle sizes. Therefore, the ideal approach is to have your welding fumes professionally sampled to determine the specific pollutants present and their particle size distribution.

This information will inform you of numerous decisions regarding your fume extraction system, guiding you in selecting the most appropriate MERV-rated filter to ensure a safe and compliant work environment.

Any questions? Ask them directly in the chat at the bottom right of your screen or during one of our webinars.

Higher MERV Ratings for Specific Pollutants

When welding involves using materials that release specific hazardous substances, a higher MERV-rated filter may be necessary for adequate protection, especially if air sampling has shown that your fume is composed of many dangerous submicronic particles.

Substances like hexavalent chromium and cadmium, recognized as carcinogens, can be present in welding fumes, especially when working with certain alloys or coatings. Manganese, another common component in welding fumes, while not a carcinogen, can still pose significant health risks affecting the nervous system with prolonged exposure.

Filters with higher MERV ratings (16 and above) are recommended for welding applications that are likely to involve these dangerous elements. Such filters have a greater efficiency (above 95%) for capturing particles as small as 0.3 to 1 micron, essential for trapping the fine particulates associated with these toxic substances.

Note on HEPA Filters: Filters with MERV-17 and higher ratings fall into the category of HEPA (High-Efficiency Particulate Air) filters. These filters are substantially more expensive due to their high efficiency. It is advisable to use them as a second filtration stage to optimize costs and prolong the life of HEPA filters. A first-stage filter can capture larger particles, thereby reducing the burden on the HEPA filter and ensuring it is reserved for the smallest and most dangerous ones.

Limitations and Regulations

While higher MERV ratings indicate a filter’s superior capability in capturing fine particles, there are limitations to what can be filtered and recirculated into the workplace. Certain substances present in welding fumes, regardless of the efficiency of the filtration system, are not safe to recirculate. Regulations sometimes mandate that fumes containing specific hazardous materials must be exhausted directly outside rather than returned indoors. See rules in the US and Canada for more information.

Compliance with these regulations is crucial, not only to adhere to legal standards but also to maintain a safe work environment. It’s essential to stay informed about the rules applicable to your operations and ensure that your fume extraction system meets or exceeds those requirements.

Conclusion

In summary, selecting the correct MERV-rated filter for welding fume extraction is a nuanced decision that can significantly impact workplace safety and health. It involves understanding the particle size distribution of welding fumes, the specific pollutants present, and the associated health risks. For welding fume filtration, MERV-13 is typically the minimum recommended. However, consider MERV-16 if you work with carcinogenic or highly dangerous substances such as manganese.

With a range of filters available, from lower MERV-rated filters for larger particles to HEPA filters for the finest particulates, the key is to choose a system that provides the necessary level of protection without being prohibitively expensive. By considering the welding processes, materials used, and sampling the fumes to determine the exact requirements, you can make an informed decision that ensures a cleaner, safer environment for all.