1、Designation: F2491 05 (Reapproved 2015)Standard Guide forDetermining Load Ratios for Technical Rescue Systems andEquipment1This standard is issued under the fixed designation F2491; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the general concept of determiningload ratios for technical rescue equipment and systems.
3、1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 In the event of any conflict between the text of this guideand any references cited, the text of this guide takes preference.1.4 This standard may involve hazardous materia
4、ls,operations, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with itsuse. It is the responsibility of the user of this standard toestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prio
5、r to use.2. Terminology2.1 Definitions of Terms Specific to This Standard:2.1.1 component, nan individual piece of equipment in itsusable form, but unconnected and unencumbered by otherpieces of equipment in a system.2.1.2 force multiplying situation, na situation where therigging causes a force on
6、a component to be greater thancaused by the load.2.1.3 load ratio, nratio between a specified breakingstrength and an anticipated load.2.1.4 strength reduction situation, na situation where therigging of the system causes a component to not perform at itsminimum breaking strength. An example would b
7、e a carabinerwith tri-axial forces.2.1.5 system, na group of components integrally con-nected for the purpose of accomplishing work.2.1.6 system safety factor, nthe ratio of the load at whichsomething in the system will fail and the load that is plannedto be applied to the system.2.1.7 user, na pers
8、on, agency, or representative who hasauthority to make safety-related decisions for rescue applica-tions as discussed herein.3. Significance and Use3.1 This guide may be used to provide a consistent methodfor determining load ratios for technical rescue equipment andsystems.3.2 Use of this guide wil
9、l help to maintain clearer, moreconsistent calculation and reporting of load ratios.3.3 It should be acknowledged that, while component loadratios are fairly straightforward to calculate, they are of limitedvalue for estimating system load ratios. System load ratios areusually desired for field appl
10、ications, but are more difficult tocalculate accurately.4. Load Ratio4.1 Load ratio refers to the ratio between the breakingstrength of the item and the load that the item is intended tosuspend.4.2 Various load ratios may be used for different reasons fora particular piece of equipment.4.2.1 A manuf
11、acturer may or may not have a specifieddesign factor, representing the ratio between the breakingstrength of the product and the working load (that is, the loadthat the product is designed to carry on a normal basis).4.2.2 Users of equipment may specify a load ratio forequipment that will help them
12、to maintain system safety factorsthat are acceptable within their own scope.4.2.3 The load ratio specified by an equipment user shall beno lower than that specified by the manufacturer, if themanufacturer specifies this information.4.3 Load ratio is applicable only to the component, and doesnot addr
13、ess how this component affects or is affected by othercomponents in a system.4.4 Load ratios, when used, should always be determinedusing minimum breaking strength as the foundation (ratherthan average or maximum or other)5. System Safety Factor5.1 System safety factor refers to the ratio between th
14、estrength of the calculated weakest point in a system and the1This guide is under the jurisdiction of ASTM Committee F32 on Search andRescue and is the direct responsibility of Subcommittee F32.01 on Equipment,Testing, and Maintenance.Current edition approved Dec. 1, 2015. Published December 2015. O
15、riginallyapproved in 2005. Last previous edition approved in 2010 as F249105(2010)1.DOI: 10.1520/F2491-05R15.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1anticipated load. This is to say that the weak point in a systemis however ma
16、ny times stronger than the load that will beplaced on the system.5.2 System safety factors are, at best, a best guess estimate,and should be used conservatively.5.3 The weakest point in a system should be determined byusing minimum breaking strengths of components as a begin-ning point.5.3.1 Other a
17、ppropriate factors that should be included inestimating the weakest point in a system include, but are notlimited to:5.3.1.1 Relationship between products (that is, how oneproduct affects another).5.3.1.2 Effects of age.5.3.1.3 Effects of environment (wet, dirty, UV, and so forth).5.3.1.4 Any other
18、known or assumed factors which mightaffect strengths.5.4 Anticipated load at any point in the system shouldreflect the amount of force that is calculated to be placed at thatpoint in a static configuration. For the same scenario, antici-pated load may vary at different points in the system.5.4.1 In
19、estimating anticipated load, consideration should begiven to at least the following factors:5.4.1.1 Mass of the load.5.4.1.2 Angle of evacuation.5.4.1.3 Directional loading.5.4.1.4 Rigging angles.5.4.1.5 Variations in the load mass (that is, addition of apatient at some point).5.4.1.6 Friction in th
20、e system.5.4.1.7 Any other known or assumed factors which mightaffect the load on the system.5.5 It may be appropriate for an equipment user to specifydifferent system safety factors for different systems. Appropri-ate safety factors for different operations may vary in accor-dance with the uncertai
21、nty of the anticipated load, or theuncertainty in the strength of the system, or consequences of afailure, or a combination of the three, among others.6. Other Requirements6.1 It is the responsibility of the user to determine accept-able load factors, whether system or component, to provideadequate
22、safety factors for his/her use.6.2 Manufacturers shall provide at least minimum breakingstrength information for any component used in life safetyapplications, in order to provide a reasonable starting point forthe user to calculate load ratios.7. Keywords7.1 equipment; load ratio; rescue; safety; s
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