1、BRITISH STANDARD BS 7527-2.5: 1991 IEC 721-2-5: 1991 Classification of environmental conditions Part 2: Environmental conditions appearing in nature Section 2.5 Dust, sand, salt mistBS7527-2.5:1991 This British Standard, having beenprepared under the directionof the General Electrotechnical Standard
2、s PolicyCommittee, was publishedunder the authority ofthe Standards Board and comesinto effect on 29November 1991 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference GEL/15 Special announcement in BSINews July 1991 ISBN 0 580 20169 4 Committees responsib
3、le for this British Standard The preparation of this British Standard was entrusted by the General Electrotechnical Standards Policy Committee (GEL/-) to Technical Committee GEL/15, upon which the following bodies were represented: Directorate of Telecommunications EEA (the Association of Electronic
4、s, Telecommunications and Business Equipment Industries) Electronic Components Industry Federation Ministry of Defence National Supervising Inspectorate Society of Environmental Engineers Society of Motor Manufacturers and Traders Limited Amendments issued since publication Amd. No. Date CommentsBS7
5、527-2.5:1991 BSI 09-1999 i Contents Page Committees responsible Inside front cover National foreword ii Introduction 1 1 Scope 1 2 Normative references 1 3 General 1 4 Natural dust and sand environments 1 5 Dust and sand in sheltered and enclosed locations 3 6 Salt mist 4 Annex A (informative) Dust
6、and sand concentrations Examples of highconcentrations 6 Annex B (informative) Bibliography 6 Figure 1 Dust and sand particle size cumulative distribution 7 Figure 2 Maximum particle size dependent on wind velocity 7 Figure 3 Occurrence of wind at a moderately windy inland site 7 Figure 4 Settling v
7、elocities for particles in still air 8 Figure 5 Sea salt distribution over land masses (average salt deposition values over the year) 9 Figure 6 Sodium chloride deposition varying with distance from the seashore (measured in Africa) 10 Table 1 Hardness scale 2 Table 2 Typical dust and sand concentra
8、tions 2 Table 3 Concentration of dust and sand at increasing altitude over deserts 2 Table 4 Major deserts 3 Table 5 Typical dust and sand sedimentation intensities 4 Table 6 Principal constituents of sea-water 4 Table A.1 Examples of high dust and sand concentrations 6 Publication(s) referred to In
9、side back coverBS7527-2.5:1991 ii BSI 09-1999 National foreword This Section of BS7527has been prepared under the direction of the General Electrotechnical Standards Policy Committee. It is identical with IECPublication721-2-5:1991 “Classification of environmental conditions Part 2: Environmental co
10、nditions appearing in nature. Dust, sand, salt mist”, published by the International Electrotechnical Commission (IEC). For the purposes of this British Standard, any references to IEC page numbers in the text should be ignored. Other Parts of this British Standard are as follows. Part 1: Environmen
11、tal parameters and their severities; Part 2: Environmental conditions appearing in nature; Section 2.1: Temperature and humidity; Section 2.2: Precipitation and wind; Section 2.3: Air pressure; Section 2.4 :Solar radiation and temperature; Section 2.6: Earthquake vibration and shock; Section 2.7: Fa
12、una and flora. Part 3: Classification of groups of environmental parameters and their severities; Section 3.0: Introduction; Section 3.1: Storage; Section 3.2: Transportation; Section 3.3: Stationary use at weatherprotected locations; Section 3.4: Stationary use at non-weatherprotected locations; Se
13、ction 3.5: Ground vehicle installations; Section 3.6: Ship environment; Section 3.7: Portable and non-stationary use. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a
14、 British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard BS 7527 Classification of environmental conditions IEC 721-1:1990 Part 1:1991 Environmental parameters and their severities (Identical) IEC 721-2-2:1988
15、 Section 2.2:1991 Precipitation and wind (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 10, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This
16、will be indicated in the amendment table on the inside front cover.BS7527-2.5:1991 BSI 09-1999 1 Introduction This section of IEC 721-2 is intended to be used as part of the background information when selecting appropriate severities of parameters relating to dust, sand and salt mist for product ap
17、plication. The severities given in IEC 721-1 should be applied. More detailed information on dust, sand and salt mist characteristics may be obtained from specialist documentation, some of which is given in the list of references in Annex B. 1 Scope This section of IEC721-2presents characteristics o
18、f dust, sand and salt mist appearing in nature, and describes the influences from these environmental factors to which products are liable to be exposed during storage, transportation and use. Although the effect of these factors is often closely associated with and at times enhanced by wind, the en
19、vironmental factor of wind is not dealt with in this section but in IEC721-2-2. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this section of IEC721-2. At the time of publication, the editions indicated were valid. A
20、ll standards are subject to revision, and parties to agreements based on this section of IEC721-2 are encouraged to investigate the possibility of applying the most recent editions of the standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards. IE
21、C721-1:1990-12, Classification of environmental conditions Part 1: Environmental parameters and their severities. IEC721-2-2:1988, Classification of environmental conditions Part 2: Environmental conditions appearing in nature Section 2: Precipitation and wind. 3 General Dust, sand, salt mist and re
22、lated wind can have an effect on products in various ways, the most important being: ingress of dust into enclosures and encapsulations; deterioration of electrical characteristics, e.g.faulty contact, change of contact resistance, change of track resistance; seizure or disturbance in motion of bear
23、ings, axles, shafts and other moving parts; surface abrasion (erosion, corrosion); clouding of optical surfaces; contamination of lubricants; reduction of thermal conductivity; clogging of ventilating openings, bushings, pipes, filters, apertures necessary for operation, etc. The presence of dust an
24、d sand in combination with other environmental factors such as water vapour can have harmful effects on products, e.g. corrosion and mould growth. Damp heat atmospheres cause corrosion in connection with chemically aggressive dust, and similar effects are caused by salt mist contained in the air. Ef
25、fects of ion-conducting and corrosive dusts, e.g.de-icing salts, may have to be considered. 4 Natural dust and sand environments 4.1 Classification of dust and sand The following definitions of dust and sand are based on different aerodynamic behaviour: dust may be defined as particulate matter of u
26、nspecified origin or composition and of size ranging from1gm to150gm. Particles of less than75gm diameter can remain suspended in the atmosphere for very long periods by natural turbulence of the air; sand is the term applied to segregated unconsolidated accumulation of detrital sediment, consisting
27、 essentially of rounded grains of quartz. The term is applied in sedimentary petrology to grains of size between1004m and10004m. Particles greater than1504m diameter are unable to remain airborne unless continually subjected to strong natural or induced air-flows or turbulence; smoke or fumes are di
28、spersive systems in air consisting of particles below1 4m. 4.2 Properties of dust and sand environments 4.2.1 Types of dust and sand The main constituent of many dusts and sands occurring in nature is quartz, causing damaging effects experienced by products in deserts and similar dusty regions. The
29、salient feature of quartz is its hardness, a property which can result in rapid wear or damage to products, particularly moving parts. However, erosion of material requires that the dust and sand are combined with a high velocity air stream or an extensive period of time. Other important characteris
30、tics of this type of dust are that it is non-absorbent and chemically inert while other types present in combination with moisture or gases in the atmosphere may have corrosive effects on metals.BS7527-2.5:1991 2 BSI 09-1999 The predominant features of fine dust are that it is often non-abrasive and
31、 hygroscopic. 4.2.2 Particle size Approximate ranges of particle size of dust and sand are: The cumulative distribution of dust and sand particle size is shown inFigure 1. 4.2.3 Particle hardness Hardness of the individual particles can determine their ability to scratch objects upon contact. Sand w
32、hich consists mainly of tiny broken chips of crystalline quartz or other mineral is generally harder than most fused silica glass compositions. Consequently, sand can scratch the surface of most glass optical devices. Pressure applied over trapped grains of sand can cause fractures to occur.Table 1
33、lists a few common substances and hardness levels according to the Mohs scale. Substances with a higher number can scratch any substance with a lower number. Table 1 Hardness scale 4.2.4 Concentrations Concentration can be measured on a mass basis, i.e.the mass of particles per unit volume of air. T
34、he concentration of dust and sand in the atmosphere varies widely with geographical locality, local climatic conditions and the type and degree of activity taking place. Under certain conditions enormous amounts of dust and sand may be released locally and temporarily from the surface while suspende
35、d dust drifts away with the wind. Table 2 indicates typical concentrations encountered in various regions within areas having a temperate climate. Table 2 Typical dust and sand concentrations Higher dust and sand concentrations are to be found under induced conditions, e.g. by helicopters and tracke
36、d vehicles as evident fromAnnex A where approximate ranges of concentrations are given. Typical dust and sand concentrations at various altitudes over deserts are shown in Table 3. Table 3 Concentration of dust and sand at increasing altitude over deserts The dust and sand concentration and the pres
37、ence of large particles are increased with increased wind speed. Figure 2 illustrates a generalization of this relationship, but this varies with several factors such as temperature, humidity, composition of particles, etc. Particles larger than1504m are in general confined to the air layer within t
38、he first metre above ground. Within this layer about half of the sand grains (by mass) move within the first10mm above the surface, and most of the other half within the first100mm. fine dust: up to75 4m coarse dust: 75 4m to150 4m sand: 150 4mm to1 000 4m Mohs scale Typical materials 1 Talcum Graph
39、ite Alabaster, diatomaceous earth 2 Gypsum Kaolinite Galena, mica, (fingernails) 3 Calcite Garite, marble, serpentine Aragonite, dolomite 4 Fluorite 5 Apatite Asbestos, opal Window glass 6 Orthoclase Magnetite, feldspar, Agate, purite, (cutlery steel) 7 Quartz Flint, fused silica, olivine Andalusite
40、, tourmaline 8 Topaz Emery 9 Corundum Sapphire, silicon carbide Tungsten carbide 10 Diamond Region Dust and sand concentration 4g/m 3 Rural and suburban 40 to 110 Urban 100 to 450 Industrial 500 to 2 000 Visibility condition Altitude Dust and sand concentration m 4g/m 3 Clear, visibility 130 km 150
41、300 600 1 200 1 800 210 220 170 140 55 Dust and sand storm, visibility 300 m, airvelocity 10 15 m/s 150 300 600 900 1 200 2 000 17 400 7 000 1 800 640BS7527-2.5:1991 BSI 09-1999 3 4.3 Factors influencing the dust and sand environment The dust and sand environment is influenced or controlled by such
42、factors as terrain, wind, temperature, humidity and precipitation. None of these factors alone will dictate whether an area has a dust problem or not; a critical combination of two or more is usually required. In the most severe, naturally occurring situations, such as in desert areas, all factors g
43、enerally have severities in the range leading to heavy concentrations of dust and sand. The physical features of the terrain can encourage strong winds of sufficient speed to cause dust and sand storms. A topographic feature such as a mountain gap increases wind velocity substantially as air is forc
44、ed through the constriction. Sand is distributed widely over the land surface of the globe. The major deserts listed inTable 4 are the primary sources of naturally occurring windblown dust and sand. The major deserts constitute about one fifth of the total land area. All continents have sandy beache
45、s of various widths, and there are large deposits of sand at or near the surface in many inland areas formerly covered by water. Table 4 Major deserts In contrast with sand, dust particles, on account of their low terminal velocity, can remain suspended in air indefinitely and may settle on surfaces
46、 anywhere. In dry conditions, soils with more than9% by mass of dust particles become at least moderately dusty and those with more than14% are potentially very dusty. Thus, as over40% of the land surface of the world, excluding the Antarctic, is classified as moisture deficient and a further40% is
47、seasonally dry, dust is expected to be present over most of the land surface of the world for substantial parts of the year. Even in regions of heavy rainfall, dust continues to create problems where the protective cover has been broken. Many moist areas are so well drained that most unprotected soi
48、l becomes dust in a remarkably short time after heavy rain. The occurrence of wind at a moderately windy inland site is shown inFigure 3. Settling velocity of particles of different size is shown inFigure 4. From this diagram assessment of settling times can be made. The effect of air currents (ther
49、mal and others) on settling times shall be considered for particles of a small size. 5 Dust and sand in sheltered and enclosed locations 5.1 Dust and sand characteristics 5.1.1 Types of dust In sheltered and enclosed locations dust materials of all kinds may be found, such as quartz, cement, flour, organic fibres, etc. 5.1.2 Particle size distribution The particle size distribution varies considerably depending on whether outdoor, driven vehicle or sheltered location is c
