| MN471004, Electrical Safety Manual Sponsor: Michael W. Hazen, 4000 |
Revision Date: June 9, 2011 Replaces Document Dated: April 29, 2008 |
This document is no longer a CPR. This document implements the requirements of Corporate Procedure ESH100.2.ELC.1, Manage Electrical Hazards.
IMPORTANT NOTICE: A printed copy of this document may not be the document currently in effect. The official version is the online version located on the Sandia Restricted Network (SRN)
Subject Matter Experts: Marc Williams and David Paoletta
MN471004, Issue K
Revision Date: March 14, 2007; Replaces Document Dated: October 9, 2006
Review Date: August 29, 2007
Administrative Changes: February 5, 2008, June 28, 2010, July 28, 2010, May 26, 2011, June 9, 2011, November 28, 2011, and February 1, 2012
This chapter provides specific electrical safety considerations for special occupancies, which include hazardous areas, explosives areas, and confined spaces. These procedures should be used in conjunction with applicable general requirements covered in Chapter 2.0, General Safety Requirements.
Hazardous areas include locations where flammable mixtures of gases or vapor, flammable liquids, combustible dust or ignitable fibers may exist. The National Electric Code (NEC) and other National Fire Protection Association codes specify and define hazardous areas in greater detail.
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There are three classes of hazardous areas. Within each class are two divisions. In general, Division 1 areas contain ignitable levels of hazardous materials under normal circumstances, and Division 2 areas are exposed to ignitable levels of hazardous materials under extreme circumstances. The requirements for Division 1 areas are more stringent than the requirements for Division 2 areas.
Areas where flammable gases or vapors are present in quantities that produce explosive or ignitable mixtures are NEC Article 501 – Class I areas. The flammable gases or vapors would include acetylene, gasoline, or turpentine.
Class I area classifications are further subdivided into groups A, B, C, and D. Group A includes only acetylene. Group B includes hydrogen and other gases. Groups C and D make up the largest groups and contain most of the petroleum fuels and solvents.
Areas where combustible dusts are present are NEC Article 502 – Class II areas. Class II area classifications are further subdivided into groups E, F, and G. Group E includes conductive metal dusts, such as aluminum and magnesium and their commercial alloys. Group F includes conductive nonmetallic dusts, such as carbon black, charcoal, coal, or coke dust with more than 8 percent entrapped volatiles. Group G includes remaining combustible dusts, such as flour, grain, wood, plastic, and chemicals.
Areas where combustible fibers are present are NEC Article 503 – Class III areas. Combustible fibers include cotton and other textile mill fibers.
To ensure that equipment in hazardous areas functions as designed, it is important to protect and clean all smoothly ground (machined) surfaces and bolted and threaded joints during assembly. Electrical equipment in hazardous areas shall conform to the requirements and special duties of these areas.
Equipment rated for a particular class is designed to contain explosions, heat and glass, and to keep out dust. This reduces the possibility of an explosion and prevents the migration of gases and dust into the enclosure
Conduit seals are fittings used in the conduit system to prevent flammable gases or combustion products from passing through the conduit. Conduit seals are extensively required in Class I areas, and are required to a much lesser degree in Class II areas.
Intrinsically safe electrical equipment is electrical equipment not capable of delivering enough energy to ignite a combustible mixture such as fumes, gases, or dusts. This equipment is generally process-related control equipment, because this equipment lends itself to low power applications.
Personnel and equipment in hazardous locations and locations where static sensitive electroexplosive devices (EEDs) are exposed shall be grounded in a manner that discharges static electricity to prevent accumulations that are capable of initiating the dusts, gases, vapors, or exposed EEDs. Permanent equipment in contact with conductive floors and table tops are not to be regarded as adequately grounded unless a separate bonded grounding conductor is in place. All grounds, including static grounds, shall be interconnected if a structure is equipped with a lightning protection system.
To determine hazardous ratings and requirements for your specific occupancy, contact the Facilities Electrical and Fire Protection Engineering Department at SNL/NM, or the Facilities Planning and Construction Management Department at SNL/CA.
Fire protection and electrical safety considerations provide criteria for a specific operation. Contact the appropriate Division ES&H team for information and permits for confined space entry. Additional information on equipment usage in hazardous areas is available in the National Electric Code (NFPA 70) 2005, the DOE Electrical Safety Handbook (DOE-HDBK-1092-2004), and in the Explosives Material Code – 26 (NFPA 495).
Areas containing explosive dusts or explosives that may, through handling or processing, produce dust capable of being dispersed in the atmosphere shall be regarded as Class II Division 1 hazardous locations.
Areas containing exposed explosives where no dust hazard exists shall be regarded as Class II, Division 2 hazardous locations as applied to permanent premises wiring as defined in the National Electric Code (NEC).
NEC definitions of Class I Division 1, and Class II Division 1 hazardous locations are modified as follows for DOE explosives facility applications:
Where explosives are processed and sublimation may occur or where flammable gases or vapor may be present in explosive or ignitable quantities, the area shall be regarded as both a Class I Division 1, and a Class II Division 1 hazard location.
To assign a space to the correct hazard class and group, you shall know the properties of the explosives involved. At a minimum, you shall know heat and spark sensitivity and thermal stability of the explosives.
If Class II Group G equipment exceeds surface temperature limits for a given hazardous area, special protection shall be provided or the equipment shall be excluded from the location. The equipment surface temperature shall not exceed the ignition temperature of the explosives.
When NEC Class I or II equipment is not available, the substitute equipment shall be purged or pressurized (in accordance with NFPA 496, Purged and Pressurized Enclosures for Electrical Equipment in Hazardous [Classified] Locations) or sealed to prevent explosives contamination. Substitute equipment shall be verified as intrinsically safe by the Facilities Electrical and Fire Protection Engineering Department at SNL/NM or the Health and Safety Department at SNL/CA. If the substitute equipment is not intrinsically safe, it shall be administratively controlled. If the substitute equipment is purged, it shall be monitored for flow.
Wiring from the permanent premises wiring to process equipment and instrumentation shall be rated for the actual environment. This shall include nonhazardous-rated ordinary locations or occupancies.
The following should be evaluated and documented by facility management for potential exposures:
If the above conditions are not evaluated, the equipment and instrument wiring will be rated automatically as Class II.
Watertight equipment shall be provided where electrical equipment and wiring may come into contact with water or explosives mixtures.
Procedures shall be established by each facility to control the use and modification of electrical equipment in explosives hazardous areas and ensure that uniform standards are adhered to throughout the facility.
Document the determination of hazard classification by the Facilities Electrical and Fire Protection Engineering Department by including the following in the written record:
Documentation will be kept by the Facilities Electrical and Fire Protection Engineering Department.
There may be multiple hazards where explosives facilities are located near electrical supply lines. To protect against these hazards, the National Electrical Safety Code (ANSI C2) and the following requirements apply to all new construction or major modifications and should be considered for existing facilities:
The electrical service entrance for explosives facilities should be provided with:
Buildings used for storage of explosives shall comply with the following electrical installation requirements:
Electrical Construction: The requirements for NEC Article 502, Class II, Division 2 permits the use of electrical metallic tubing, intermediate or rigid conduit, liquid tight conduit, dust-tight boxes and dust-tight wireway.
Live parts shall not be exposed in Class II, Division 2 locations. Switches, motors and other electrical devices shall be made dust-ignition proof.
Preferred Location: The preferred location of service equipment, switchboards, and panel boards is in a separate, less hazardous, positively pressurized room.
Current Surges: Electrical installations in packaged explosives storage spaces shall include protection from large currents, such as surge, ground fault, or lightning. To prevent arc-producing and potentially damaging currents from entering the structure, surge protectors and lightning arrestors are required for incoming conductors. Electric lines serving an explosives facility shall be installed underground at least 50 feet from the facility.
All other electric distribution lines shall be no closer to the facility than the line distance between two poles. An interconnected grounding system and a “green wire” ground system are required.
Lightning Protection: Lightning protection should conform with the NFPA 780 Lightning Protection Code. Frequent preventive maintenance inspections for grounding and lightning protection should be performed by facilities maintenance personnel.
An interval of seven months for visual maintenance inspections and a 14-month interval for resistance measurements inspections are recommended. This ensures that maintenance inspections occur in all seasons of the year and at periodic intervals. These inspections are documented by the Electrical Maintenance Services Department.For questions concerning explosives operations, contact the Explosives Safety Engineering Department at SNL/NM or the Facilities Planning and Construction Management Department at SNL/CA.
For additional requirements and guidance of explosives operations, see the Explosives Safety Manual, MN471011.
Confined spaces may contain extremely hazardous atmospheres due to little natural air movement. Confined spaces can contain oxygen-deficient atmospheres, flammable atmospheres, or toxic atmospheres.
Employees who work in a confined or enclosed space that contains exposed energized parts shall use protective shields, protective barriers, or insulating materials, as necessary, to avoid inadvertent contact with these parts.
Doors, hinged panels and the like shall be secured so they cannot swing into personnel and cause them to come into contact with exposed energized parts.For assistance in determining confined space requirements, contact the Industrial Hygiene Program at SNL/NM or the Health and Safety Department at SNL/CA.
For additional information on Confined Spaces, including worker qualification requirements, see ESH100.2.IH.9, Enter Confined Spaces Safely.
This section is being developed. It will address the use of electrical equipment in arctic weather.
Marc Williams, mwilli4l@sandia.gov
Darrell Fong, dfong@sandia.gov