Playing It Intrinsically Safe
Intrinsic safety is a protection standard employed in potentially explosive atmospheres. Devices that are certified as "intrinsically safe" are designed to be unable to release sufficient energy, by either thermal or electrical means, to cause ignition of flammable material such as gases, dust and particulates.
Intrinsically safe standards apply to all equipment that can create one or more of a range of defined potential explosion sources:
- Electrical sparks.
- Ionizing radiation.
Intrinsic safety is particularly important for technicians working in industries such as petrochemical, pharmaceutical and pulp/paper, or around bulk materials such as grain, mining or any environment where explosive gases are present.
The importance of safety in these environments cannot be stressed enough. It takes a very small amount of energy to cause an ignition -- for example, a mixture of hydrogen in air requires only 20 microJ of energy. The proper practices and tools will minimize the inherent risk involved in working around these hazards.
Standards OrganizationsWhile Europe has taken the lead in regulating intrinsically safe standards, several organizations have had intrinsically safe guidelines in place for some time. The standards groups include ATEX, IEC, Factory Mutual and OSHA.
ATEX. The primary intrinsically safe regulations were set in the European Union with the 94/9/EEC Directive, commonly called ATEX ("Atmospheres Explosibles," French for explosive atmospheres). The stated goal of the guidelines is to "help ensure the free movement of products in the European Union" by "minimizing the number of safeguard clause applications, at least those originating from divergent interpretations." The intent of 94/9/EEC is to serve as a total harmonization directive, laying down essential health and safety requirements, and replacing existing divergent national and European legislation that covers the same subjects.
ATEX rules have been in place as a voluntary standard since March 1, 1996, but they became mandatory on electrical and electronic equipment for use in environments subject to explosion hazard sold in the EU starting July 1.
IEC. The International Electrotechnical Commission is responsible for setting international standards for electrical technology. Its technical committee TC31, which deals with explosion protection for electrical apparatus, has introduced a procedure, the IECEx Scheme, that is intended to become a globally recognized test and certification procedure for explosion protection.
Historically, obtaining all of the necessary national safety certifications for electrical products used in explosive atmospheres has been a difficult, time-consuming and expensive proposition. In the Ex Scheme, the IECEx accredits Accepted Certification Bodies (ACBs) to test and certify conformity of electrical equipment used in explosive atmospheres with internationally harmonized product safety standards and issue "Ex" test certificates and test reports. This approach is not unlike the IEC requirements for using certified bodies for the CB European Union marking scheme for CE compliance throughout the harmonized countries of Europe.
There are currently 17 ACBs in 22 countries participating in the IECEx Scheme, including the United States and Canada. For multinational companies that are concerned with intrinsic safety in the workplace, IECEx certification provides assurance that the equipment purchased meets the safety standards across many if not all the countries in which they have facilities.
Factory Mutual. In the United States, Factory Mutual Research, managed by Factory Mutual (FM) Global, is a not-for-profit scientific and testing organization that has tested and certified more than 40,000 products in the last 165 years. Factory Mutual N.I. Class 1, Division 2 areas Group A to D is the most frequently referenced U.S.-based intrinsic safety standard and arguably the best reference for U.S. manufacturing engineers.
NEC. The National Fire Protection Association (NFPA) 70, National Electrical Code, also known as the NEC, is the basis for all electrical codes in the United States. Classifications and related product markings for hazardous areas are covered in NEC 500 and 505. These are similar to, but not exactly the same as, those in ATEX.
OSHA. The Occupational Safety & Health Administration (OSHA) of the U.S. Department of Labor participates in the US-EU Cooperation on Workplace Safety & Health. This is a project of the U.S. DOL, OSHA and the EU European Agency for Health and Safety at Work. The goal is to promote sharing of information on current safety and health topics of common interest.
Intrinsic safety is covered under Regulations (Standards - 29 CFR), Hazardous (classified) locations 1910.307 and 1926.407. OSHA references the NEC guidelines (500) 70-339 Hazardous Locations, 501 Class I Locations, 502 Class II Locations, 503 Class III Locations, 504 Intrinsic Safe, 505 Class I, Zones 0, 1, and 2 for determining the type and design of equipment and installations that will meet this requirement.
Identifying the DangersWith all the attention various standards organizations have made to intrinsically safe guidelines, there isn't a single, universal set of standards for manufacturing engineers to reference. The key for manufacturing engineers who are concerned with intrinsic safety is to identify the areas of potential hazard -- any area with flammable gases, dust, or particulates -- as well as the processes and devices that might trigger an explosion. Once identified, implementing the appropriate levels of safety processes and using the appropriate tools will ensure worker safety.
For example, a common maintenance routine that poses a risk of explosion is the calibration of 4 to 20 mA process loops. The keys to safely performing a loop calibration in potentially explosive environment are strict adherence to calibration procedures and the use of a loop calibrator that is certified to meet the intrinsically safe standards set by at least one of the standards organizations. The basic procedure includes:
Make sure the system is shut down and other workers are notified that a potentially dangerous operation will be taking place.
Similar procedures can be implemented for other processes that could be dangerous. The answer is to arm yourself with information on intrinsic safety by reading the guidelines set by Factory Mutual or other safety organizations, audit your facilities and processes to identify potential dangers, and use intrinsically safe-certified tools and equipment in any environment where the risk is high. With a few, carefully considered processes and tools, it is relatively easy to safeguard the working area and minimize the risks involved in potentially explosive environments.