Proper light levels on construction sites are critical to worker productivity and jobsite safety.
OSHA Standard 1926.56 outlines the safe minimum light levels for various areas of operation within a jobsite. For example, general construction areas require a minimum of 5-foot candles, while mess halls require 10, and office areas or first aid stations require 30 foot-candles.
But how do we design our worksites to meet OSHA's minimum standards in hazardous areas?
First, we need to know about the space or atmosphere that we are lighting from a hazardous-location perspective. Through rigorous testing, UL has developed environmental classifications around the hazardous atmospheres these spaces might contain. Understanding these atmospheres is critical to the hazardous lighting fixture selection and wiring methods necessary to power the fixtures.
Per Article 500 of the National Electrical Code, an area is considered a hazardous location when there are (or may be) ignitable concentrations of combustible substances in the air. These substances include vapors, dust, certain fibers and flammable gases. Through rigorous testing, UL has separated the atmospheres (spaces) into three distinct categories based on the primary hazardous material present in each:
- Gases, vapors or liquids
- Dusts
- Fibers and filings
Next, there are groups (A-G), which list the specific hazardous material present in a space, followed by divisions (1 or 2), which list the conditions in which the hazardous material exists in the atmosphere (normally present, suspended or used, not normally present, and suspended or stored).
Explosion-proof lighting is a special type of product designed to withstand the toughest environments, specifically hazardous locations. To be considered explosion- proof, a lighting fixture must be able to contain an internal combustion by preventing it from propagating outside the unit.
Many people assume that these fixtures work via a seal around the bulb (and its other components), which prevents flammable compounds from entering the device. However, that's only half the story. Explosion-proof lighting contains a unique feature called a "flame path," which is a special type of joint between different parts of the enclosure. A flame path is essentially a controlled leak that allows expanding gases from an internal explosion to cool and safely vent to the outside without igniting any explosive atmosphere that may be present outside the lamp. The class, division and group that the enclosure is rated for determines the allowable leak rate (flame path gap and length) to prevent external ignition. For example, a Group A enclosure for acetylene has a much smaller leak rate than a Group D enclosure for propane.
It is worth noting that products that are appropriate in hazardous areas are not always explosion-proof. There are many other methods to mitigate explosion risk. Other techniques include intrinsic safety, encapsulation, oil immersion, pressurization, etc., depending on each application's specific needs. Project managers should review a product's certifications prior to bringing it to the jobsite to ensure the equipment is appropriate for its specific application.
Now that we've determined the minimum amount of lighting for a given space and that space's atmospheric condition, here is where the science of lighting is applied. The Illuminating Engineering Society has recommendations for several workspaces and developed requirements and standards against which manufacturers test their fixtures and publish the data of their results. Lighting designers use this data with lighting software to design a particular space, considering the size of the area to be illuminated, mounting height, surface reflectance and minimum light levels. These figures, combined with fixture performance, will provide the number of selected fixtures and spacing necessary to achieve the desired lighting level in the selected area.
Understanding the atmosphere of the space to be lit and minimum lighting levels for safe and efficient working conditions are essential to selecting, designing, and applying lighting to achieve a safe and productive workspace.
For more information and to read Ericson's blog, visit www.ericson.com or call (800) ERICSON [374-2766]. For questions about hazardous area lighting design, contact Brian Earl at (440) 477-0331.
