1、Designation: F 2491 05Standard Guide forDetermining Load Ratios for Technical Rescue Systems andEquipment1This standard is issued under the fixed designation F 2491; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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.1.2 The values
3、stated in SI units shall be considered asstandard. Values in English units may be included for refer-ence.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 materials, opera-tions, a
4、nd 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 prior to use.2. Term
5、inology2.1 Definitions of Terms Specific to This Standard:2.1.1 componentan individual piece of equipment in itsusable form, but unconnected and unencumbered by otherpieces of equipment in a system.2.1.2 force multiplying situationa situation where therigging causes a force on a component to be grea
6、ter thancaused by the load.2.1.3 load ratioratio between a specified breakingstrength and an anticipated load.2.1.4 strength reduction situationa situation where therigging of the system causes a component to not perform at itsminimum breaking strength. An example would be a carabinerwith tri-axial
7、forces.2.1.5 systema group of components integrally connectedfor the purpose of accomplishing work.2.1.6 system safety factorthe ratio of the load at whichsomething will fail and the load that is planned to be applied tothe system at that point.2.1.7 usera person, agency, or representative who hasau
8、thority 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 will help to maintain clearer, moreconsist
9、ent 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 applications, but are more difficult tocalc
10、ulate 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 manufacturer may or may not have a specified
11、design 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 to maintain system safety factorsthat a
12、re 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 address how this component affects or is af
13、fected 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 thestrength of the calculated weakest poi
14、nt in a system and theanticipated load. This is to say that the weak point in a systemis however many times stronger than the load that will beplaced on the system at that point.1This guide is under the jurisdiction of ASTM Committee F32 on Search andRescue and is the direct responsibility of Subcom
15、mittee F32.01 on Equipment,Testing, and Maintenance.Current edition approved April 1, 2005. Published April 2005.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 System safety factors are, at best, a best guess estimate,and should
16、 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 appropriate factors that should be included inestimating the weakest point in a system are limited, but notlimited to:5.3.1.1 Relationship
17、 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 known or assumed factors which mightaffect strengths.5.4 Anticipated load at any point in the system shouldreflect the amount of force th
18、at 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 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 eva
19、cuation.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 the 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 u
20、ser to specifydifferent system safety factors for different systems. Appropri-ate safety factors for different operations may vary in accor-dance with the uncertainty of the anticipated load, or theuncertainty in the strength of the system, or consequences of afailure, or a combination of the three,
21、 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 safety factors for his/her use.6.2 Manufacturers shall provide at least minimum breakingstrength information for any component used in li
22、fe safetyapplications, in order to provide a reasonable starting point forthe user to calculate load ratios.7. Keywords7.1 equipment; load ratio; rescue; safety; safety factorASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentio
23、nedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee an
24、d must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting o
25、f theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box
26、 C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).F2491052
