AWS F3 2-2018 Ventilation Guide for Weld Fume (2nd Edition).pdf

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1、AWS F3.2:2018An American National StandardVentilation Guidefor Weld FumeAWS F3.2:2018An American National StandardApproved by theAmerican National Standards InstituteDecember 14, 2017Ventilation Guide for Weld Fume2nd EditionSupersedes AWS F3.2M/F3.2:2001Prepared by theAmerican Welding Society (AWS)

2、 Project Committee on Fumes and GasesUnder the Direction of theAWS Committee on Safety and HealthApproved by theAWS Board of DirectorsAbstractThis document introduces the reader to various types of ventilation systems, including general supply and exhaust andlocal exhaust, for control of weld fumes.

3、 It contains or refers to information on air contaminants found in welding fumes,principles of system design and selection, and drawings that illustrate ventilation techniques.iiAWS F3.2:2018 ISBN: 978-0-87171-944-7 2018 by American Welding SocietyAll rights reservedPrinted in the United States of A

4、mericaPhotocopy Rights. No portion of this standard may be reproduced, stored in a retrieval system, or transmitted in anyform, including mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyrightowner.Authorization to photocopy items for internal, perso

5、nal, or educational classroom use only or the internal, personal, oreducational classroom use only of specific clients is granted by the American Welding Society provided that the appropriatefee is paid to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, tel: (978) 750-8400; In

6、ternet:4000 ft/min (20 m/s) and high pressure 60 in water gauge (WG) (1520 mm WG), but at a low air volume, typically75 ft3/min300 ft3/min (125 m3/hr510 m3/hr) when using 1 in3 in (25 mm75 mm) diameter hose or duct. These sys-tems require very large extraction units or pumps to create the high opera

7、ting pressure. Typical types of extractiondevices include suction nozzles, welding guns with integrated fume extraction and flex hoses. The extraction systemhoses and duct sizes are generally very small and can be easily moved about the work area or used in restricted spaces.Also, due to the low vol

8、ume of air movement, make-up or outside air introduced back into a space that a ventilation sys-tem has exhausted outside, is kept at a minimum.Low vacuum systems can be source extraction, local or general ventilation. Low vacuum source extraction systems drawair from a close proximity, 6 in15 in (1

9、50 mm380 mm) from the welding arc. The equipment is designed such that itremoves a large volume of air at low transport velocity 2000 ft/min3000 ft/min (10 m/sec15 m/sec) and low pressure4 in20 in WG (100 mm500 mm WG). Welding fume extraction arms typically operate at 400 ft3/min1000 ft3/min(680 m3/

10、hr1700 m3/hr) with a diameter of 6 in8 in (150 mm200 mm). Downdraft tables, backdraft registers and can-opy hoods operate at levels based on their design. The larger in surface area that the table or canopy hood is, the more airvolume required to maintain adequate efficiency and effectiveness.In eit

11、her the high or low vacuum systems, factors that influence the type and design of the extraction system includewelding process, work envelope, application, weldment, extraction device design, and system performance. The posi-tioning of the extraction source is dependent on the welding application, m

12、anufacturing process, ambient air conditions,and the volume the system extracts. The further away the exhaust system inlet is positioned from the fume generatingsource, the more air volume must be applied to capture the fume and remove it from the work zone. These systems willonly be effective if th

13、ey are correctly designed, installed, maintained, and operated.Table 1Local Exhaust VentilationTypeDistance from Arcin (mm)Volume Rangeft3/min (m3/hr)Static PressureWater Gauge (WG)in (mm)Duct Diameter in (mm) Noise LevelLow Vac 615 (150380) 4001000 (6801700) 420 (100500) 68 (150200) LowHigh Vac 26

14、(50150) 75300 (125510) 60 (1520) 13 (2575) HighAWS F3.2:20185The choice of local ventilation system type depends on the method and conditions of welding, type of welding equip-ment, size of welded components and shop space factors. Typical systems are shown in Table 2 and Figures 1 through 8.As a ge

15、neral rule, it is recommended that the welding zone or welding room have a slight negative pressure. This is toallow for additional clean air seepage into the welding areas and to reduce the possibility of any contaminated air migrat-ing into other nonwelding areas of the facility such as administra

16、tive offices, learning centers, or other occupied spaces.General ventilation uses contaminant-free air to dilute the airborne contaminants not captured by local exhaust. Localexhaust systems can evacuate some of this contamination and the rest can be evacuated from the building by the generalexhaust

17、 or ventilation systems.5.3 General Ventilation5.3.1 Types of General Ventilation Systems. General ventilation systems are also considered low-vacuum or high-volume systems as they displace a large amount of air. The general ventilation system is designed to remove contami-nants from the ambient air

18、 within the facility and therefore may not protect the welders breathing zone.Table 2Local Ventilation Systems for Welding and Cutting ProcessesSystem Type Typical Airflow Comments ReferenceWelding gun withintegral fume extraction30 ft3/min60 ft3/min(50 m3/h100 m3/h)Extracts fume at the weld zone th

19、rough GMAW and FCAW guns.Figure 1High vacuum source capture nozzle75 ft3/min300 ft3/min(125 m3/h510 m3/h)Captures fume through high-velocity, low-volume extraction nozzles. Usually positioned by the welder.Figure 2Flexible fume extraction arm400 ft3/min1000 ft3/min(680 m3/h1700 m3/h)Draws higher air

20、 volume and is easily positioned and repositioned by the welder.Figure 3Cross-draft weldingtable (slotted hood)180 ft3/min280 ft3/min per ft2(3300 m3/h5000 m3/h per m2)Excellent for controlling fume in a fixed location serving small part welding.Figure 4Fixed exhaust hood 1470 ft3/min1760 ft3/min(25

21、00 m3/h3000 m3/h)Used for overhead capture in fixed locations. Figure 5Push-pull hood over welding robotVaries with hood height and space An engineered design to reduce exhaust air volume in a large, fixed welding zone.Figure 6Canopy hood Varies with hood design Uses larger air volumes to control an

22、 area where source capture is impractical.Figure 7Downdraft cutting table 150 ft3/min per ft2(2700 m3/h per m2)Used in large, fixed, flat plane operations. Figure 8General Notes:Figure 3. Individual flexible extraction arms can be connected to a single fan or multiple arms can be connected to collec

23、tion/fan exhaust system.Extraction arms can also be incorporated into a mobile or hanging unit with a built-in filter and fan. The type of support mechanism and hose lengthmay allow a lateral positioning radius of up to 30 ft (9 m) at heights of up to 18 ft (5.5 m) above the floor.Figure 4. A cross-

24、draft table can be open or enclosed on the sides and top to form an open-front box. Air is extracted through rear slots or grilles.Figure 6. The push-pull hood over a welding robot is an alternative to a gun-mounted extractor or a large canopy hood over the welding area. Toreduce the amount of exhau

25、st and replacement air, the push-pull hood combines air recirculation and slot diffusers to create an air curtain around thewelding area. An air cleaner is recommended to allow partial recirculation.Figures 6 and 7. These systems are best for robotic (nonhuman) applications since they draw contamina

26、ted air through the welders breathing zone.Figure 8. When using a downdraft table, ensure that large work pieces do not block the full surface of the tabletop.AWS F3.2:20186Figure 1Welding Gun with Integral Fume ExtractionFigure 2High-Vacuum Source Capture NozzleAWS F3.2:20187Figure 3Flexible Extrac

27、tion ArmsFigure 4Cross-Draft Welding Table with Slotted HoodAWS F3.2:20188Figure 5Fixed Exhaust HoodFigure 6Push-Pull Hood over Welding RobotAWS F3.2:20189Figure 7Canopy HoodFigure 8Downdraft Cutting TableAWS F3.2:201810General ventilation includes the use of roof exhaust fans, wall exhaust fans, an

28、d other large air moving devices.Although this type of ventilation is not usually as effective as local exhaust systems in removing fumes, especially fromthe welders breathing zone, it is often helpful if used in addition to local exhaust ventilation to capture the residual fumethat passes the local

29、 ventilation device and rises to the ceiling in most welding environments. Local and general ventila-tion systems can work well together and complement each other in the removal of welding fumes within the occupiedwork zone. General ventilation brings fresh air into the work environment, dilutes fum

30、es and gases, and exhausts theminto the atmosphere. General ventilation systems (supply and exhaust) can be mechanical, natural, or mixed (mechanicalsupply, natural exhaust, or vice versa). When there are no special demands for thermal comfort conditions in the build-ing during the cooling and heati

31、ng season, natural ventilation through the windows, doors, or fixed air vents can be used,as long as contaminant concentration in the breathing zone is controlled. When seasonal control is needed due to closeddoors and windows, a mechanical supply (make-up) air system is required to deliver fresh ai

32、r into the work space.5.3.2 General Supply Systems. Mechanical supply systems are normally used for contaminant dilution and thermalcomfort in the occupied zone. They consist of inlet sections, filters, heating and/or cooling equipment, fans, ducts, andair diffusers for distributing air within the s

33、hop. One form of general supply ventilation systems is what is termed “push-pull” systems. There are several variations of these systems, but typically the system extracts the contaminated air wherethe welding fume plume hovers, draws it into a filter to remove the contaminant and reintroduces the a

34、ir into the occu-pied workspace at floor or ceiling level. This approach would work in applications such as welding on large structuresand robotic welding cells, typically where the welding work zone is large and the weld length is constantly changing.These systems may also aid in temperature contro

35、l of the facility.5.3.3 General Exhaust Systems. General exhaust systems complement local exhaust systems by removing air con-taminated by fumes, gases or particles not captured by local exhaust systems. Such systems usually consist of inlets,ducts, an air cleaner (filter), and a fan. In welding sho

36、ps, general exhaust inlets tend to be located at points higher thanother air moving devices. Since the welding plume tends to rise in welding shops, general exhaust inlets are located inthe upper zone. The efficiency of the air cleaner must be sufficient to meet the regulations of safety and environ

37、mentalagencies, and may be affected by location, concentration of contaminants in the atmosphere, nature of contaminants,height, and velocity of the air-discharge stack. In some cases, the air cleaners may be excluded from the general exhaustsystem and general exhaust can be provided by the wall or

38、roof fans.5.3.4 Recirculation. When hazardous gases and particles have been sufficiently removed, it may be possible to recir-culate part or all of the air cleaned in the general exhaust system, which will reduce heating and cooling costs. In thiscase, a return duct is used to bring the shop air to

39、the supply unit, or the air is cleaned in free-hanging air filter units. Por-table units are also used for isolated or point of fume generation control with the cleaned air recirculated directly backinto the area being served.Airflow rates for general ventilation should reflect not only the key cont

40、aminants in the occupied zone (not captured bythe local ventilation system) but also the heating and cooling demands of the space.In order to recirculate, steps should be taken in order to avoid accumulating contaminants in the workplace environment;safeguards need to be designed into the ventilatio

41、n system based on the process, procedures, and materials to be used inthe facility and implemented by the building owner or operator. In addition to OSHAs occupational safety and healthregulations, state OSHA programs may have additional requirements for recirculation of process exhaust air, and loc

42、albuilding codes may be applied by local authorities having jurisdiction (AHJ). Consequently, a review of the potentialrisks, hazards, and applicable requirements should be made during the design phase of the project to determine the feasi-bility of recirculating the welding fume exhaust. The follow

43、ing measures should be considered and implemented whenappropriate:(1) Hazard evaluation and assessment by a competent industrial hygienist;(2) Special precautions for exhaust air with acutely toxic, highly toxic or carcinogenic materials;(3) Specification of air cleaning equipment;(4) Methods and eq

44、uipment to be used to identify the contaminants generated during normal and upset conditions;(5) Responses, equipment and procedures to assure worker protection during an upset condition;(6) Facility owner and management responsibility for a higher level of preventive maintenance and operational int

45、eg-rity than a conventional exhaust system; and(7) Air contaminant monitoring program to evaluate actual usage and potential worker exposure after system installation.AWS F3.2:201811Further guidelines have been established in ANSI/ASSE Z9.7, American National Standard for the Recirculation of Airfro

46、m Industrial Process Exhaust Systems. This standard sets the criteria for the design and operation of a recirculatingindustrial process exhaust ventilation system used for contaminant control. The purpose of the standard is to create min-imum guidelines to:(1) Determine if the air that contains cont

47、aminant can be sent through an air cleaning system and safely recirculatedwithin the occupied space;(2) Determine if correct methods and equipment are being used to identify the contaminants generated by a processduring typical and high particulate generation conditions; and(3) Address possible heal

48、th and safety problems if recirculation is to be used.The standard describes system configuration, health evaluation and analysis, material requiring special precautions(such as hexavalent chromium (CrVI), system discharge, air cleaning equipment, multiple contaminants, continuousmonitoring device s

49、ystem monitor, maintenance, record keeping, and signs.5.3.5 Outside Exhaust Systems. When a contaminant is exhausted outside of a facility, environmental regulationsmust be considered. Among these are Metal Fabrication Hazardous Air Pollutants (MFHAP)National Emissions Stan-dard for Hazardous Air Pollutants (NESHAP) Rule, 40 CFR Part 63 Subpart XXXXX. These rules apply to the collec-tion equipment and activities necessary to perform welding operations which use MFHAP, or have the potential to emitMFHAP. EPA has requirements to reduce the emi