Consulting-Specifying Engineer - November 2007 - (Page 36)

• Cleanroom-rated fixtures must be specified • Cleanroom lighting levels must meet an average of 100 ft candles on the ground and at each maintenance catwalk • Lamp failures caused by acoustical and vibration tests should be eliminated • No out-gassing materials, including silicone, should be used in the lighting fixtures • Explosion-proof lighting must be used from the ground floor up to 14 ft above the floor • Ballasts for all fixtures should be remotely mounted • Maintenance of the lighting system should be as simple as possible. The challenge The industrial setting posed three challenges: the cleanroom environment, the hazardous environment on the ground floor and the high sound/vibration environment. Lighting manufacturers do not perform acoustic or vibration tests on their equipment. In addition, no standard judges how well lighting equipment will withstand a certain sound level. Select fixtures, however, are manufactured for use in environments that have higher levels of vibration and shock. To determine an appropriate solution, the team examined two different lighting systems manufactured for use in similar environments. The first system is a cleanroom-rated light fixture containing an induction fluorescent lamp rated at 150 W and 12,000 lumens. This fixture was chosen as an option because of its ability to withstand high vibrations, including installation under train platforms for the Chicago rail system. Table 1: Induction fluorescent fixtures Advantages Induction lamp provides long life and is proven to withstand high-vibration environments. Quality of fixtures will provide more overlap and create fewer shadows. Disadvantages Remote ballast distance limited to 66 ft. Quantity of fixtures is high due to wattage limitations of the induction lamps. Engineers chose floodlights for this high-bay environment because this light fixture is manufactured for high-vibration, hazardous environments without modifications. Photo courtesy The RMH Group The light fixture contains a small amount of silicone in the induction lamp housing, but will not out-gas and the ballasts can be remotely mounted at a distance of up to 66 ft. See Table 1. Given that the ballasts for the lowest row of fixtures are above the top of the chamber at a vertical distance of 57 ft from those fixtures, it was likely that the ballasts for the lower rows of fixtures are in an adjacent space. The additional horizontal distance to that adjacent space would be greater than 66 ft. The second option is a metal-halide floodlight rated at 400 W and 34,000 lumens. Made for the mining industry, the light fixture contains a vibration-dampening lamp socket supported by a multi-plane diaphragm to absorb shock and vibration, and is rated for both clean rooms and hazardous environments. The ballasts also may be remotely located 75 ft or closer without any issues, and the lights located near the catwalks to allow for ease of maintenance. The lamp socket and lens gasket contain high-temperature silicone and EPDM rubber, but do not out-gas. See Table 2. Design conclusion The team recommended floodlights because this light fixture is manufactured for high-vibration, hazardous and clean-room environments without modification. In addition, the lower quantity of light fixtures would be less expensive to install, and the fixture count and locations would more closely match existing conditions, allowing the contractor to reuse much of the existing conduit and wire. Also, costs associated with the decreased lamp life would be offset by the lower maintenance costs. The end user agreed, but also thought that light output consistency should be given greater weight. The end user requested a hybrid design using the Class 1, Division 2 floodlights at the ground floor where the hazardous environment exists and the incandescent fluorescent light fixtures at levels 2 through 5. Within a year the chamber had undergone five full-cycle vibration and acoustic test cycles, and most of the incandescent fluorescent light fixtures showed some signs of failure. Fixtures are cleanroom-rated and use felt Fixture locations and quantities are difficult gasketing to eliminate out-gassing. to maintain. Light fixtures are listed for hazardous environments with modifications to standard light fixtures. Small amount of silicone is used in induction lamps. Light fixture material costs is about $110,000, about $33,000 more expensive than metalhalide floodlights. 36 Consulting-Specifying Engineer • NOVEMBER 2007

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Consulting-Specifying Engineer Contents Editor's Viewpoint Letters In The News M/E Roundtable Emergency Power for Healthcare 2007 Products of the Year Industrial-strength Lighting Hazardous HVAC Codes and Standards Management Report Jobs/Classifieds Specifier's Notebook On-Peak Performance Contents Best Battery Selector in Engine Starting Applications NEC 708: Practical Impact on Backup Power Systems Protecting Power: Specifying Outdoor Generator Enclosures Investing in Backup Power Systems Coes, Consultants, Manufacturers, and Standby Power Systems

Consulting-Specifying Engineer - November 2007

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