In 2020, the AIHA Mining Working Group (MWG) reviewed and provided technical input on the development of ISO 23875, Mining – Air Quality Control Systems for Operator Enclosures – Performance Requirements and Test Methods. This equipment design consensus standard was developed by the International Organization for Standardization’s Mining Technical Committee (ISO TC 82) and was published in February 2021. MWG’s participation meshed perfectly with our goal of advocating for improved standards that support occupational health protection in the mining industry.

Although the new ISO 23875 is an equipment design standard and not one directly relating to health, safety, or the environment, it has significant implications for the occupational health of mining equipment operators. ISO 23875’s development introduced a significant opportunity for the occupational health community to better protect worker health and safety in the mining sector.

THE CREATION OF ISO 23875 ISO standards can be thought of as internationally developed “formulas” that assimilate best practices. They are intended to represent the distilled wisdom of people with expertise in their subject matter who know the needs of the organizations they represent. These experts include representatives from manufacturers, sellers, buyers, customers, trade organizations, users, and regulators. ISO has published more than 21,500 standards, has members in 162 countries, and includes 788 technical bodies for standard development. AIHA MWG’s expertise, which includes that of manufacturers, regulators, insurers, and health and safety personnel who work directly for or in support of the mining industry, was well suited to contribute to the new standard’s development.

The scope of the ISO TC 82 Mining Technical Committee includes standardizing specifications relating to machinery and equipment used in open-cast metal and nonmetal mines and all underground mining machinery and equipment used for the extraction of solid mineral substances. ISO TC 82 is also responsible for creating standards related to the presentation of mine survey plans and drawings, methods for calculating mineral reserves, mine reclamation management, the design of structures for the mining industry, special refuge and rescue chambers, and shaft boring machines.

In total, the ISO TC 82 Mining Technical Committee is directly responsible for 52 ISO standards plus six currently under development, and the committee has contributed to at least five more. Within TC 82 are working groups (WGs) and subcommittees (SCs) that address specific mining subjects, including mine closure and reclamation management, advanced automated mining systems, rock drill rigs, tailings, structures for mine shafts, terminology, and operator enclosures. Working Group 9 was responsible for developing ISO 23875.

The standard specifies performance and design requirements for air quality control systems for operator enclosures and their monitoring devices. The design specifications are intended to meet identified parameters of pressurization and concentrations of respirable particulate and carbon dioxide. The standard also specifies test methods to assess these parameters and provides operational and maintenance instructions. Gases and vapors that can be a hazard in the work environment outside of the operator enclosure are excluded from this initial version of the standard but may be considered for future revisions.

ISO provided the AIHA MWG an initial version of the standard that included sections on performance requirements; engineering design; air quality control monitoring device requirements; and system testing, operation, and maintenance. Also included were annexes that provide guidance on management of carbon dioxide, which is generated by respiration of miners within an operator enclosure, as well as recommendations for operational integration of the standard. The annexes mimic the nonmandatory appendices within some OSHA regulations.

The operator enclosure performance requirements included in the standard detail parameters of carbon dioxide, respirable particulate, and pressurization to ensure an effectively operating enclosure. The carbon dioxide parameter is defined in terms of decay time and maximum sustained concentration, the respirable particulate parameter is defined in terms of maximum concentration, and the pressurization parameter is defined in terms of maximum sustained pressurization.

The standard also details design requirements for the air quality control system. These general requirements include elements of required pre-filtration and filtration, minimizing noise levels, cabin pressurization, ease of performing routine maintenance, anticipation of HVAC system leakage, external air supply using a plenum, and continuous operation of these systems.

In July 2020, 16 members of the MWG formed a project team to review the content and develop proposed changes and enhancements to the standard.

THE IMPORTANCE OF OPERATOR ENCLOSURES Participating in the development of this standard presented a significant opportunity for the occupational health community. NIOSH estimates that from 1971 to 2019, almost $50 billion in federal compensation was paid to miners and their families for claims filed under the Black Lung Benefits Act, which benefits those disabled from pneumoconiosis arising from their employment in or near mines. Published studies have confirmed that respiratory ailments resulting from occupational exposures related to mining activities, although not always curable, are almost always preventable through the implementation and maintenance of effective engineering interventions.

NIOSH has concluded that occupational exposure to respirable crystalline silica is associated with silicosis, lung cancer, pulmonary tuberculosis, and airways diseases. In addition, it may be related to development of autoimmune disorders, chronic renal disease, and other adverse health effects. However, a World Health Organization fact sheet on silicosis from 2000 states that occupational occurrences of these diseases in silica-exposed workers are preventable and admonishes that “action should be taken before exposure happens.”

These realities have necessitated the development of a diverse approach to reducing health risks associated with silica, coal dust, and other chemical exposures in mining operations, including the use of well-designed and managed operator enclosures. Accordingly, operator enclosures are an integral part of NIOSH’s most important publications on dust control in mining: Best Practices for Dust Control in Coal Mining, Best Practices for Dust Control in Metal/Nonmetal Mining, Diesel Aerosols and Gases in Underground Mines: Guide to Exposure Assessment and Control, and Dust Control Handbook for Industrial Minerals Mining and Processing.

In its 2010 publication, Best Practices for Dust Control in Coal Mining, NIOSH stated that “enclosed cab filtration systems are one of the mainstay engineering controls for reducing mobile equipment operators’ exposure to airborne dust at surface mines.” The publication goes on to cite effective protection factors ranging up to 89 for use in rock drilling. Key performance factors are identified as including cab enclosure integrity (for example, maintaining seals on doors, engine cowls, and windows), pressurization, use of high efficiency particulate air (HEPA) filters on air supplies, use of recirculation dust filters, effective housekeeping, and keeping cab doors and windows closed. These factors were also discussed in NIOSH’s publication, Best Practices for Dust Control in Metal/Nonmetal Mining, released the same year.

Diesel Aerosols and Gases in Underground Mines: Guide to Exposure Assessment and Control was published the following year. In it, NIOSH further acknowledged that

Finally, in the 2019 second edition of the Dust Control Handbook for Industrial Minerals Mining and Processing, NIOSH expanded this content on enclosed cabs with an entire section on filtration and pressurization systems for environmental enclosures. This section provides a deeper look at operator enclosures and pressurization systems, wind penetration, recirculation filtration, and secondary design considerations including air inlet locations, heating systems, maintenance and housekeeping, the ease of filter changing, filtration efficiency, and system monitoring and maintenance tracking capabilities.

NIOSH’s work has brought operator enclosures into more consistent and effective use in industrial minerals mining and processing operations. The agency’s guidance documents complement the development of ISO 23875 and its requirements.

AIHA MWG’S CONTRIBUTIONS The AIHA MWG project team used the ISO’s process for providing comments on ISO 23875. All comments were consolidated; then, the project team members reviewed the comments and determined, by consensus, which comments would be forwarded to ISO TC 82 Working Group 9. In total, the project team offered 30 comments and proposed changes. The working group accepted 12 of them, sometimes with a variation to the proposed change; 17 were determined to be out of the standard’s scope, to be considered in its next revision, or were not accepted for other reasons; and 1 comment was selected for further consideration by the ISO editor. The standard was published in February 2021, and there are already discussions within the TC 82 working group regarding the next revision, which is anticipated to include gas filtration parameters for operator enclosures.

The MWG project team’s feedback focused greatly on the standard’s engineering design section, which addresses air quality control systems, external air and recirculation airflow systems, considerations for filter and filter housing design, and handling instructions for filter media. The project team suggested changes related to air filter orientation (for example, making reverse installation difficult or less likely), maintenance, and replacement; air monitoring device usage; and supplemental air filtration and environmental control system enhancements. Most of the MWG’s commentary and input arose from the members’ field experience during the design, manufacture, and use of mining equipment under real-world circumstances.

ISO 23875’s section on the engineering design of the operator’s enclosure addresses the recommended design objective of an enclosure’s air quality control system: that is, using filtration and pressurization to prevent respirable particulate matter in the ambient mine environment from entering the operator’s enclosure. A primary concern is that leakage from low-pressure areas in the HVAC and the external filtration systems may cause airborne fugitive particulates to enter the operator enclosure without passing through the external HEPA air filtration system. A component of this design objective is to ensure that the operator enclosure remains pressurized by the air quality control system whenever a miner operates the equipment.

MWG also offered input regarding the use of materials for interior surfaces that allow for easy housekeeping; the use of materials that do not introduce other, unintended hazards (for example, by minimizing the potential for products of thermal decomposition under heat load); isolating engine exhausts from locations of designed air intakes; and addressing noise levels in the design phase of operator-enclosed mining equipment. Although ISO ultimately deemed that some of MWG’s input was out of scope for the initial version of the standard, it may be incorporated into future revisions.

An additional element of the standard addresses the capability of the enclosure to effectively circulate a supply of external air to the operator cab and monitor for effectiveness using measured concentrations of carbon dioxide. The standard further supports usage of carbon dioxide data in its annex on carbon dioxide management. MWG members’ experience in field application and problem-solving from challenges that arise during actual field use conditions was particularly helpful in reviewing this material.

The standard’s other annex on recommendations for operational integration of ISO 23875 recognizes the successful operation and maintenance of operator enclosure systems are ultimately up to the end user of the equipment. This annex addresses retrofitting of operator enclosures, operation and maintenance of performance test equipment, operating air quality control systems, maintaining operator enclosures and air quality control systems, and additional air quality control considerations.

As with many standards, there is opportunity to broaden the scope and content of ISO 23875 through future revisions. The AIHA MWG has established a Category C liaison status with the ISO TC 82 working group that will allow the MWG to comment on future revisions of the standard. In the meantime, the MWG’s efforts have furthered its mission to optimize the health and safety of miners, wherever they may work, and the MWG looks forward to collaborating, communicating, supporting, and contributing to the development of new consensus standards.

Acknowledgment: The authors thank Alyssa Ehman, MSc, CIH, of Aura Health and Safety Corporation for reviewing this article.

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