• Author / Uploaded
• zhigang ding

Citation preview

COOLING TECHNOLOGY MANUAL

Chapter 12

FIELD-ERECTED COOLING TOWER FIRE PROTECTION

COOLING TECHNOLOGY INSTITUTE PO Box 73383 Houston, Texas 77273 281.583.4087 Fax: 281.537.1721 http://www.cti.org email: [email protected]

March 2010

Chapter 12 (10)

1

FOREWARD This Cooling Technology Institute (CTI) publication is published as an aid to cooling tower purchasers and designers. It may be used by anyone desiring to do so, and efforts have been made by CTI to assure the accuracy and reliability of the data contained herein. However, CTI makes no warranty of fitness for particular purpose or merchantability nor any other warranty expressed, implied or statutory. In no event shall CTI be liable or responsible for Incidental, Consequential or Commercial losses or damage of any kind resulting from this publication's use; or violation of any federal, state, or municipal regulation with which this publication may conflict or for the infringement of any patent resulting from the use of this publication. All CTI codes and standards are copyrighted with all rights reserved to CTI. The reproduction of any part of this or any other CTI code or standard is a violation of Federal Law. One must recognize and appreciate commitment by a number of volunteer members who donate their time to develop and update CTI codes and standards. The monies spent for code development, administrative staff support and publication are essential and constitute a substantial drain on CTI. The purchase price of these documents helps to offset these costs. Reproduction and distribution by others, in addition to being unethical, undermines this system and constitutes a further financial drain on CTI. When copies are needed, you are requested to call or write the Cooling Technology Institute, P.O. Box 73383, Houston, Texas 77273, (281) 583-4087. Please request that your associates buy the required codes and standards rather than copy them. Your cooperation in this matter is greatly appreciated. Nothing contained herein is to be construed as granting any right for the manufacture, sale or use in connection with any method, apparatus, or product covered by letters patent, nor as insuring anyone against liability for infringement of letters patent. This guideline document summarizes the best current state of knowledge regarding the specific subject. This document represents a consensus of those individual members who have reviewed this document, its scope and provisions. It is intended to aid all users or potential users of cooling towers.

Approved by the CTI Executive Board.

This document has been reviewed and approved as part of CTI's Five Year Review Cycle. This document is again subject to review in 2014.

Approved by the CTI Executive Board

Copyright 2010 by Cooling Technology Institute Printed USA

2

March 2010

Field-Erected Cooling Tower Fire Protection Table of Content Paragraph Title

Page

1.0

Scope

5

2.0

Definitions

5

3.0

Cooling Tower Fire Hazards

6

4.0

Fire Risk Analysis

6

5.0

Fire Protection Options

6

6.0

Design and Material Choices

7

7.0

Bibliography

7

3

4

Field-Erected Cooling Tower Fire Protection 1.0 Scope This section provides fire protection considerations for field erected cooling towers. 2.0 Definitions 1. Fire Protection - The prevention and reduction of hazards associated with fires. This process includes the study of fire behavior, suppression, and investigation of the fire as well as the research and development, production, testing, and application of mitigating systems. 2. Combustible Material - A material that under design conditions will ignite and burn and does not meet the definition of noncombustible or limited-combustible. 3. Limited-Combustible Material - Either a noncombustible material with a surfacing of no more than 1/8” that has a flame spread rating of 50 or less or selfextinguishing materials with a flame spread rating of 25 or less. 4. Non-Combustible Material - A material that under design conditions will not ignite, burn, support combustion, or release flammable vapors. All materials which have passed ASTM E-136 are non-combustible. 5. Fire Resistance - The property of a material or assembly to withstand fire or provide protection from a fire. 6. Fire Resistant Wall - A tight, continuous wall that is suitable for use in a cooling tower environment that has a fire resistance rating of twenty minutes or more. The partition must extend from one foot below the operating water level of the cold water basin to the underside of the fan deck and/or distribution basin. The test for the wall must be performed in accordance with NFPA 251. Examples of walls that meet this requirement include: 12.7 mm (1/2 in) cement board, 12.7 mm (1/2 in) plywood, and 19.1 mm (3/4 in) tongue and groove boarding that are installed on both sides of wood studs and in accordance with NFPA 251. 7. Fire Resistance Rating - The time in minutes or hours that materials or assemblies have withstood a standard fire exposure. The rating should be determined in accordance with the NFPA 251 and NFPA 221, 2000ed. 8. Self-Extinguishing - The ability of a material to cease burning once the igniting flame source is removed. 9. Fire Wall Test Specimen per NFPA 251 - The test specimen must be a true representation of the construction for which the fire resistance rating is to be determined with respect to materials, workmanship, and details such as dimension of parts. The wall must be built under conditions representative of those properties that are applied in actual building construction and operation. 10. Twenty Minute Fire Wall - The wall assembly must have withstood the fire endurance test without passage of

11.

12.

13.

14.

15.

16.

17.

18. 5

flame or gases hot enough to ignite cotton waste for a period of time equal twenty minutes. Note: The fire resistance wall is an assembly test of materials as the materials would be in an actual installation. The twenty minute fire wall is a NFPA 251 code. Thirty Minute Fire Wall - The wall assembly must have withstood the fire endurance test without passage of flame or gases hot enough to ignite cotton waste for a period of time equal thirty minutes. Note: The fire wall is an assembly test of materials as would be in an actual installation. The thirty minute fire wall is a NFPA 251 code. Sprinkler System - A system of piping and nozzles designed to control or extinguish fires. The system includes a network of piping and sprinklers which are interconnected. The system also includes one or more automatic water supplies. Wet Pipe System - A sprinkler system employing automatic sprinklers attached to a piping system containing water and connecting to a water supply so that water discharges immediately from sprinklers opened by heat in a fire. Dry Pipe System - A sprinkler system employing automatic sprinklers attached to a piping system containing air or nitrogen under pressure, the release of which permits the water pressure to open a valve known as a dry pipe valve. The water then flows into the piping system and out the opened sprinklers. Pre-Action System - A sprinkler system employing automatic sprinklers attached to a piping system containing air that may or may not be under pressure, with a supplemental detection system installed in the same areas as the sprinklers. Actuating of the detection system opens a valve that permits water to flow into the sprinkler piping system and to be discharged from any sprinklers that may have opened. Deluge System - A sprinkler system employing open sprinklers attached to a piping system connected to a water supply through a valve that is opened by the operation of a detection system installed in the same areas as the sprinklers. When the valve opens, water flows into the piping system and discharges from all sprinklers attached thereto. FM Tower - A cooling tower and all its components that have been examined from a fire prevention standpoint and evaluated for the quantity or toxicity of combustible products and found to be a low fire hazard. A tower does not require an automatic sprinkler system when installed using the materials and components that were tested and approved by Factory Mutual. Flame Spread Rating (Surface Burning Characteristics Rating) - The numerical rating of a material calculated

from the results of a tunnel test. The rating indicates the relative rate at which flame will spread over the surface of the material as compared with flame spread on asbestoscement board which is rated 0 and on red oak which is rated 100. 19. Test Method (Tunnel Test) - The test used to obtain results from which a rating is calculated. It is commonly referred to as the tunnel test as the testing equipment is a twenty-five foot tunnel. 20. ASTM E-119 (Assembly Test) - This is an assembly test not a product test. This is the test method used for fire resistance assemblies. The test exposes a wall assembly to standard fire conditions controlled to achieve specified temperatures throughout a specified time period. The fire exposures are typically followed by a standard hose stream test which subjects the specimen to impact erosion and cooling effect of water stream.

3.

4.

5.

3.0 Cooling Tower Fire Hazards Field erected cooling towers that are constructed completely, or in part, of combustible materials can support proliferating internal files. Overheating of the fan motor can start a fire. Depending on the material, the fill may be another fire hazard present in most cooling towers. Wood fill is combustible, polypropylene and polyethylene are combustible even with fire retardants, and PVC is self-extinguishing and has limited combustibility. Human error is also a contributing factor; smoking, hotwork that was not appropriately managed, and overloading electrical circuits are examples. Then there are the outside the cooling tower sources of fire hazards such as incinerators, smokestacks, or lightning. The wet environment created by cooling tower operation does not negate the associated fire hazards. Fires can spread internally within a cooling tower during periods of operation as well as periods of maintenance or construction when the cell is not in operation. Some types of cooling towers are even more susceptible to fire hazards because of the dry areas within the cooling tower.

6.

7.

Is the cooling tower located next to another structure or building? Does the cooling tower have limited access because of the tower’s location that would hinder fighting a fire? Water supply Is there an adequate water supply with which to fight a fire? Climate Are there extreme temperatures that would affect fighting a fire? Construction materials No fire protection is required if the cooling tower’s structure, fan deck, distribution deck, louvers, and fill materials are noncombustible. Limited Combustibles Material falls in a gray area that you should consult your company’s insurance group to determine the type of protection required. (See limited combustible material definition.) The type of tower Crossflow or counterflow? It is more difficult to provide fire protection for a crossflow cooling tower. Value of the tower This is an owner judgment. How important is this tower to the job site?

5.0 Fire Protection Options Now that the fire risk analysis has been completed by the cooling tower owner, the materials necessary to achieve the degree of desired fire resistance for the cooling tower can be determined. Once the degree of fire resistance is determined, then fire prevention options are selected. Options to be considered for fire protection: 1. Structural framework • Concrete Structural; considered non-combustible • Steel Structural; considered non-combustible • FRP Pultruded Structural; Fire-retardant, selfextinguishing with a flame spread rating of 25 or less per ASTM E84 Flame Spread Test • Wood Structure; considered combustible Note: Douglas Fir lumber has a spread rating of 70 to 100 per ASTM E84 Flame Spread Test 2. Exterior and Partition Walls • Concrete; considered non-combustible • Steel; considered non-combustible • FRP; Fire-retardant, self-extinguishing with a flame spread rating of 25 or less per ASTM E84 Flame Spread Test Note: 20 minute fire wall per NFPA 251 Wood; considered combustible Note: Douglas Fir ½ plywood has a spread rating of 130 to 150 per ASTM E84 Flame Spread Test 3. Fan Deck • Concrete; considered non-combustible

4.0 Fire Risk Analysis Before fire protection can be determined for a cooling tower, a fire risk analysis should be performed. This will allow the cooling tower owner to rank the importance of the cooling tower remaining in operation at all times. The following are some of the factors that should be considered when determining the method of fire protection for the cooling tower. 1. Importance of continuous operation Does the cooling tower need to be in operation most of the time in order to meet cooling requirements set by the tower owner? If not, what will be the duration and frequency of inactivity? 2. Location of cooling tower 6

4.

5.

6.

7.

• Steel; considered non-combustible • FRP; Fire-retardant, self-extinguishing with a flame spread rating of 25 or less per ASTM E84 Flame Spread Test • Wood; considered combustible Fill Media • Ceramic; considered non-combustible • PVC; Fire-retardant, self-extinguishing with a flame spread rating of 15 or less per ASTM E84 Flame Spread Test • Wood Lath; considered combustible Distribution Header • FRP; Fire-retardant, self-extinguishing with a flame spread rating of 25 or less per ASTM E84 Flame Spread Test Drift Eliminators • Ceramic; considered non-combustible • PVC; Fire-retardant, self-extinguishing with a flame spread rating of 25 or less per ASTM E84 Flame Spread Test Fan Stack • Concrete; considered non-combustible • FRP; Fire-retardant, self-extinguishing with a flame spread rating of 25 or less per ASTM E84 Flame Spread Test

3.

4.

5.

1.

6.0 Design and Material Choices Note: The following examples of fire protection are a sample of the fire protection combinations available in the market. The examples are listed in order from the least fire protection choice to the greatest fire protection choice. 1. Douglas Fir Tower Note: Douglas Fir lumber has a spread rating of 70 to 150 per ASTM E84 Flame Spread Test. 2. Fire-retardant, self-extinguishing FRP structure with fire retardant, self-extinguishing internals and fire walls per NFPA 251

2. 3.

4. 5.

7

Note: Fire resistant wall is a constructed wall that has passed an assemble test not just the materials being used. FRP fire retardant self-extinguishing structure with fire retardant self-extinguishing internals and fire resistant wall per NFPA 251 and Deluge sprinkler system per NFPA 13. This combination will provide a higher degree of protection where water supplies are adequate. Note 1: Materials used must be similar to that which has been specified for the cooling tower based on the environmental demands of the cooling tower. Note 2: Due to the inaccessibility of the piping during normal operation of the cooling tower, it is virtually impossible to perform maintenance work or routine inspections. The corrosion problems have the potential to be serious in water cooling towers, and leaks in the system are not readily apparent. FM Cooling Tower Per Factory Mutual Research Corporation’s Cooling Tower, System Components Approval Guide, Chapter 12 Concrete or steel structures with non-combustible materials for internals such as concrete fan stacks, steel drift eliminators, ceramic tile fill, and fire retardant distribution header. 7.0 Bibliography National Fire Protection Standard No. 214, “Standard for Water Cooling Towers”, 1971 National Fire Protection Association Standard No. 13, “Installation of Sprinkler Systems”, 1991 National Fire Protection Association Standard No. 251, “Standard Methods of Tests of Fire Resistance of Building Construction and Materials”, 2006 ASTM E119-00a, “Standard Methods of Tests for Fire Tests of Building Construction and Materials”, 2004 Factory Mutual Research Corporation, “Cooling Tower, System Components, Chapter 12”, 2007

COOLING TECHNOLOGY INSTITUTE PO Box 73383 Houston, Texas 77273 281.583.4088 Fax: 281.537.1721 http://www.cti.org email: [email protected] 8