Consulting-Specifying Engineer - November 2007 - (Page 42)

and operations costs. International Fire Code (IFC) Table 2703.1.1 states that basic quantities of materials are allowed in control areas without taking extraordinary design measures. However, if the standard allowable quantities are exceeded, the design needs to comply with a host of requirements to meet code. That being said, quantities of allowable materials are classified in three ways: storage, useclosed systems, and use-open systems. In general, larger quantities of materials are permitted in storage and use-closed than in use-open systems. To classify an installation as storage or use-closed, the system or containers must not be opened at any time during normal activities. Depending on the material, the maximum allowable quantities can be limited, particularly for the open-use classification. According to IFC Table 2703.1.1 footnotes, quantities of some materials may be doubled with installation of an approved automatic fire suppression system. In some cases, storage classification quantities may be doubled again when the hazardous materials are kept in an approved storage cabinet, gas cabinet, exhausted enclosure, or safety cans. Deflagration venting may need to be specified when a hazardous material listed in IFC Table 911.1 exceeds the Table 2703.1.1 quantities. Also known as blast walls, deflagration venting prevents unacceptable structural damage and limits the potential for occupant injury, but adds significant cost to a project. Spaces equipped with deflagration venting resists a minimum internal pressure of 100 lb per sq. ft as the vented wall or roof relieves at a maximum internal pressure of 20 lb per sq. ft. Limiting quantities may save on first costs, but ongoing production and maintenance costs may be incurred due to more frequent transporting, stocking, and handling activities. Also, disconnection and connection of tanks and piping will likely classify the system as open-use and constrain the quantities allowed for production. At the same time, workarounds may be possible. For example, in a solvent cleaning lab removable flammable liquid storage tanks were classified as closed systems by using dry-link couplings.These couplings provide fa drip-free connection to supply piping and are manufactured from a variety of materials for chemical compatibility with the hazardous material. By classifying the solvent supply tanks as a closed system, the team increased the allowable quantities. Those quantities were doubled again by protecting the area with an automatic sprinkler system. In the end, this approach also avoided costly deflagration venting of the room. The code also allows for other approaches to increase allowable quantities within a control area. For instance, a mixture of different solvents can be collected and pumped to solvent waste containers after the solvents have been applied to the manufactured product. These containers are considered open-use because they require an unobstructed vent as they are filled. As with the solvent supply containers, the waste containers also need to be disconnected, removed, and reconnected in the control area. Locating the waste containers in a room with automatic fire suppression can increase the allowable quantities by as much as 100%. Thus, it is advisable to capture open-use container fumes by placing containers in a vented enclosure, which can be either off-the-shelf or custom-fabricated to meet the constraints of the area. In either case, an average 100 fpm air velocity must be maintained across the face of the hood boundary. This velocity can equate to a significant amount of air depending on the size of and needed accessibility to the containers. To reduce the required air flow, which has a direct relationship to operating energy costs, sliding doors can reduce the face area of the hood. See Figure 1. Incidentally, hazardous occupancies require a significant amount of air to maintain a clean and safe environment. In accordance with code, with Figure 1 This fume hood shows a sliding door. Duct velocity should be minimum 1,200 fpm. Source: The RMH Group the minimum ventilation requirements relating to six air changes per hour with a 10-ft ceiling, control areas exceeding the allowable quantities of hazardous materials must be ventilated at a minimum of 1 cfm/sq. ft. Also, ventilation may need to be increased to account for capture hoods, other process equipment, and if the area is a classified clean space. Ventilation requirements based on local exhaust hoods and process loads generally meet the requirements for a clean space, depending on the cleanroom class one is trying to achieve. As a point of reference, typical room velocities and air change rates for different classes of cleanroom are shown in Table 1. If contaminates are captured and exhausted from the Table 1 Air changes per hour vs. vertical airflow velocities, room heights and cleanliness classes Air changes per hour for ceiling height (ft) ISO Class 2 3 4 5 6 7 8 9 FS209 Class 1 10 100 1,000 10,000 100,000 1,000,000 Velocity (fpm) 85-100 70-85 60-70 45-55 25-35 8-16 4-6 2-3 8 638-750 525-638 450-525 338-413 188-263 60-120 30-45 15-23 10 510-600 420-510 360-420 270-330 150-210 48-96 24-36 12-18 12 425-500 350-425 300-350 225-275 125-175 40-80 20-30 10-15 16 319-375 263-319 225-263 169-206 94-131 30-60 15-23 8-11 If contaminates are captured and exhausted from space, then recirculated air may be acceptable. Air dilution calculations help determine if the amount of ventilation and recirculated air will dilute the environment to safe levels. Source: The RMH Group 42 Consulting-Specifying Engineer • NOVEMBER 2007

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - November 2007

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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