Conformity assessment in the USA

Author: Thorsten Arnhold, Wolfgang Berner

Image 1: Control panel in conduit technique for hazardous areas

A few years ago, that title would almost certainly have been "Conformity assessment in North America". However, since Canada has gradually adapted its national regulations since then to match IEC/IECEx practice, the following information refers only to conformity assessment in the USA.

In contrast to the international IEC/IECEx community and the European Union, the conformity assessment landscape in the USA is very heterogeneous, both generally and for explosion protection in particular. From the governmental side, three authorities are responsible for the safety standards for hazardous areas:

OSHA – Occupational Safety and Health Administration: Industrial plants on the mainland
MSHA – Mine Safety and Health Administration: Mining facilities
US Coastguard: Offshore facilities in the coastal waters of the USA

Only the US Coastguard permits the direct use of products with an IECEx certificate in hazardous areas of offshore facilities as one possible procedure.

To simplify the explanation of this very complex topic, this section will only discuss the areas regulated by OSHA; the methods used by MSHA and the US Coastguard are very similar to those used by OSHA.

OSHA is an agency within the United States Department of Labor. Its activity focuses on safety in the workplace. Part of its work involves establishing mandatory rules; it is also responsible for education, training, and public relations on the topic of occupational safety (1).

The US Occupational Safety and Health Act (OSH Act) makes employers responsible for providing their employees with a safe workplace that is also free from anything that could damage their health, including in the long term. As well as complying with this general clause within the Act, employers must also comply with all relevant OSHA standards.

As documents issued by the government, these OSHA standards are, to a certain extent, comparable to European directives, although the objective and level of detail of the technical requirements differ significantly. For instance, no relatively abstract framework requirements regarding safety, such as those in Appendix II of ATEX 2014/34/EU, are established. Instead, workplace-specific technical requirements are set out and must always be complied with. Additionally, OSHA standards do not deal with commissioning (providing) equipment; the OSHA standards apply to the employer, who is obligated to demand that their suppliers comply with the requirements in the standards. The following OSHA standards apply specifically to equipment that is intended for use in hazardous areas:

29 CFR Part 1910 Subpart O "Machinery and Machine Guarding" (2)
29 CFR Part 1910 Subpart S "Electrical" (3)

These standards recommend, with respect to general electrical safety or to electrical equipment and its wiring in hazardous areas for instance, that the devices and machines installed and operated in this area are tested and listed by a Nationally Recognized Testing Laboratory (NRTL). The Nationally Recognized Testing Laboratory (NRTL) programme means that commercial organisations can be recognised and qualified to perform testing and certification processes for specific products as an independent third party. Each NRTL is accredited by OSHA with respect to specific standards for product safety tests. Currently, 20 NRTLs have been certified by OSHA (4). In principle, the legislator does not stipulate which NRTL must approve a specific product. Officially, all NRTLs are of equal importance when it comes to workplace safety in the USA. However, the test body Underwriter Laboratories (UL) also plays a significant role thanks to its high degree of international recognition and general reputation.

Image 2: Conduit Installation for hazardous areas

"UL-certified" is frequently used colloquially as a synonym for the testing and certification processes performed by an OSHA-accredited body. In the past, the phrase "PTB-certified" had similarly valuable connotations in Germany. In addition, UL (like Factory Manual, FM) itself also issues product standards, which all NRTLs must use as a basis for their assessments.

After a product has passed the testing and certification processes performed by an NRTL, the respective manufacturer is authorised to mark the product with the registered logo of the testing and certification body. Alongside the logo, a list of the standards that the product complies with is also provided.

For an external onlooker, trying to get to grips with the sheer number of additional regulatory organisations in the USA is always disorienting. The hierarchies and links between the different standards are also tricky to grasp. The set of rules that establish the safety of technical products, such as machines or electrical equipment, can be seen as a combination of national laws, fire codes, electrical guidelines and product standards.

As well as OSHA, a number of state-level and private organisations are responsible for maintaining and issuing a range of documents:

National Fire Protection Association (NFPA)
American National Standards Institute (ANSI)
American Society for Testing and Materials (ASTM)
Institute of Electrical and Electronics Engineers (IEEE)
Food and Drug Administration (FDA)
Federal Communications Commission (FCC)
International Society of Automation (ISA)
Underwriters Laboratories (UL)

The most well-known regulatory document in the electrical safety sector is ANSI/NFPA 70® – National Electrical Code (NEC) (27). This has been issued by the National Fire Protection Association since 1911 and is revised every three years. Essentially, the NEC handles the general underlying principles and regulations regarding the safety of people and systems, including:

Protection against electric shock
Protection against thermal influences
Protection against overcurrents and overvoltages
Protection against residual currents
Mechanical safety

Chapter 5, which deals with the topic of "special occupancies", is particularly important for explosion protection.

Article 500 contains a general description of the regulations that must be complied with in hazardous areas; it also sets out the process of categorising areas into classes and divisions:

Class I: Areas in which combustible gases, vapours and mists consisting of combustible liquids may be present in dangerous quantities
Class II: Areas in which combustible dusts may be present in dangerous quantities
Class III: Areas in which easily ignitable fibres may be present in dangerous quantities

In turn, these classes are each divided into two divisions, depending on the likelihood of dangerous quantities of the aforementioned combustible substance being present(similar to the three zones in the IEC classification):

Division 1: Constant to occasional presence of a hazardous explosive atmosphere (i.e. combines Zones 0 and 1 into a single category)
Division 2: Rare, brief presence of a hazardous explosive atmosphere due to rare faults in the system

Image X: Comparison of zones according to IEC and divisions according to NEC, including the probability limits used in some countries (MIC) ratio.

Article 500 also contains a classification system for the different combustible substances.

For instance, Group A refers to acetylene. The combustible substances in Groups B, C and D include gases and vapours; they differ according to their minimum ignition energy, expressed using the minimum gap width and the minimum ignition current (MIC) ratio.

Combustible dusts are categorised in Groups E, F and G. Combustible metallic substances belong in Group E, coal dusts in Group F, and other combustible dusts in Group G.

Finally, Article 500 also outlines potential types of protection for Divisions 1 and 2; it also sets out some general requirements for devices, such as classification of surface temperatures.

Articles 501 to 504 cover the specifications for installation methods in Class I to Class III. Article 504 sets out the requirements for intrinsically safe systems. Articles 505 and 506 explain how IEC zone classification can be used for systems in the USA. Article 510 contains specifications for special operations, such as garages, repair workshops, aircraft hangars, and more.

The individual requirements established by the NEC are set out in more detail using the standards listed here. The organisations listed above are responsible for creating these standards.

Alongisde ANSI/NFPA 70 NEC, ANSI/NFPA 79 Electrical Standard for Industrial Machinery is also very important for machinery and equipment manufacturers in particular.

The beginning of this section referred to the extreme heterogeneity of the conformity assessment landscape in the USA; this is partly due to the number of different regulatory organisations involved, and partly dependent on the monitoring practices that apply in each state, district and community within the country. Compliance with the range of applicable standards and regulations is the responsibility of the "Authorities Having Jurisdiction" (AHJs). Depending on the regulation that has priority locally, these may include:

State Electrical Commission
State Fire Marshal
Department of Public Safety

A machine or system may only be commissioned if it has been granted an operating licence by an AHJ of this kind. The fact that these decisions are not made in an equivalent way across the USA is purely because different US states refer to different issues of the NEC.