Power Lines and the WUI

Photo from: LA Times

As fires continue to rage throughout California, investigations into the twelve fires that occurred earlier this year, and burned 245,000 acres, have been concluded. Investigators with Cal Fire have determined that these fires were caused by Pacific Gas & Electric Company power lines. High winds in the area caused trees and branches to fall onto the lines, and in at least one case a power pole failed and collapsed. PG&E currently has a vegetation control program in place with a budget of $400 million per year.

NFPA 1, Fire Code provides clear guidance on how to prevent fires from electrical lines. Chapter 17, Wildland Urban Interface outlines the following  requirements for vegetation clearance around electrical transmission and distribution lines, conductors, and their appurtenances.

• 10 feet clearance is required around all poles or towers
• At the time of trimming, the following minimum clearances should be provided based on the line voltage:

• As the growth returns, it is permitted to grow to within the clearances shown in the table below. Once this minimum distance is reached vegetation must be trimmed back to the required minimum clearance.

                             

• The AHJ has authority to adjust clearance requirements based on local needs or conditions, and vegetation type

NEC Hazardous Locations

Though many jurisdictions have electrical inspectors that enforce the provisions of NFPA 70, National Electrical Code (NEC), there are provisions and requirements that overlap with the duties of the fire inspector. Some of these areas or occupancies include high hazard industrial facilities, paint rooms and spray booths, hazardous materials storage, and fuel handling processes and operations. These areas require that the fire inspector properly classifies the hazardous location in order to ensure proper installation of electrical wiring and components.

NFPA 70, Article 500 defines these hazardous classifications as follows, “Locations shall be classified depending on the properties of the flammable gas, flammable liquid–produced vapor, combustible liquid–produced vapors, combustible dusts, or fibers/flyings that could be present, and the likelihood that a flammable or combustible concentration or quantity is present. Each room, section, or area shall be considered individually in determining its classification.”  These are divided into classes and divisions.

Class I - locations in which flammable gases, or flammable or combustible liquid-produced vapors are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures.

Class II - locations that are hazardous because of the presence of combustible dust.

Class III - locations that are hazardous because of the presence of easily ignited fibers, or where combustible flyings are handled, manufactured, or used.

The charts below show the Class and Divisions categories.

Download the "NEC Hazardous Locations - Quick Reference" sheet here.

*Group E. Atmospheres containing combustible metal dusts, including aluminum, magnesium, and their commercial alloys, or other combustible dusts whose particle size, abrasiveness, and conductivity present similar hazards in the use of electrical equipment.

In some instances a “zone” designation may be used as an alternative to the division classification system shown here. These zones will either be Zone 0, Zone 1, Zone 2, or Zone 20, Zone 21, Zone 22. These are defined in NFPA 70, Article 505 and Article 506.

Article 505 defines Class 1, Zone 0, Zone 1, and Zone 2 as “locations where fire or explosion hazards may exist due to flammable gases, vapors, or liquids.” Article 506 defines Zone 20, Zone 21, and Zone 22 as “locations where fire and explosion hazards may exist due to combustible dusts or ignitable fibers/flyings.”

As a tool for the field inspector or plans examiner we have created a single page reference that provides quick access to the classification and division definitions.

Download Now - "NEC Hazardous Locations - Quick Reference" sheet

Electrical Safety

The fire code offers very specific regulations regarding extension cords, surge protectors, and wiring in commercial structures.

NFPA 1:11.1 Electrical Fire Safety

11.1.5.2
Multiplug adapters shall not be used as a substitute for permanent wiring or receptacles.


11.1.6.2
The relocatable power taps shall be directly connected to a permanently installed receptacle.

11.1.6.3
Relocatable power tap cords shall not extend through walls, ceilings, or floors; under doors or floor coverings; or be subject to environmental or physical damage.

11.1.7.1
Extension cords shall be plugged directly into an approved receptacle, power tap, or multiplug adapter and shall, except for approved multiplug extension cords, serve only one portable appliance.

11.1.7.3

The extension cords shall be maintained in good condition without splices, deterioration, or damage.

 

11.1.7.5

Extension cords and flexible cords shall not be affixed to structures; extend through walls, ceilings, or floors, or under doors or floor coverings; or be subject to environmental or physical damage.

11.1.7.6

Extension cords shall not be used as a substitute for permanent wiring.

Check out this great post concerning electrical safety at the office, from All Business.