Appropriate ventilation and fume extraction in welding shops

Transcription

1 This document is downloaded from the Digital Open Access Repository of VTT Title Appropriate ventilation and fume extraction in welding shops Author(s) Kulmala, Ilpo Citation 68th IIW Annual Assembly and International Conference, IIW2015, 28 June - 3 July 2015, Helsinki, Finland, Welding Society of Finland (2015), presentation slides, 26 p. Date 2015 Rights This presentation may be downloaded for personal use only. VTT P.O. box 1000 FI VTT Finland By using VTT Digital Open Access Repository you are bound by the following Terms & Conditions. I have read and I understand the following statement: This document is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of this document is not permitted, except duplication for research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered for sale.

2 VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD IIW 2015 The 68th IIW Annual Assembly and International Conference Helsinki, Finland June 28 - July 3, 2015 Ilpo Kulmala Appropriate Ventilation and Fume Extraction in Welding Shops

3 Contents Contaminant control measures Ventilation systems Local ventilation Capture efficiency Design of LEV systems General ventilation Air distribution Ventilation energy consumption Summary 01/07/2015 2

4 Contamination control measures 01/07/2015 3

5 Hierarchy of control measures Elimination Substitution Replacement of the welding process with an alternative joining technique Modification of welding processes to generate less fumes Isolation Ventilation Automating and isolating the welding operation Local ventilation General ventilation Personal protective equipment Powered filtering helmet 01/07/2015 4

6 Welding shop ventilation systems 01/07/2015 5

7 Ventilation system Consists of local and general ventilation General exhaust General ventilation - Controls air temperature and humidity - Dilutes contaminants not captured by the local exhaust system - Replaces exhausted air Local exhaust - Removes contaminants at their source 01/07/2015 6

8 Local exhaust ventilation systems 01/07/2015 7

9 Local Exhaust Ventilation Removes contaminants at the source before they are released into the workplace air Creates controlled air flows towards the exhaust hood Components: Hood to capture the contaminants Ducting to transport the contaminants Fan to provide sufficient air flow rate Discharge 01/07/2015 8

10 Types of welding fume extractor solutions Central Low Velocity High Volume extraction Portable fume extractor with built-in filter and fan (HVLV) Welding bench hood Fume Extraction Gun 01/07/2015 9

11 Capture efficiency LEV performance is characterised by capture efficiency, which is defined as the percentage of emissions directly captured by the exhaust ventilation Ambient air currents Efficiency 01/07/

12 Measured capture efficiencies for Shielded Metal Arc Welding Capture efficiency (%) ACGIH recommended values for welding exhaust: m/s ( fpm) These correspond to measured capture efficiencies 85 - >95% Air velocity (m/s) 01/07/

13 Velocity fields generated by exhaust hoods High velocity low volume (HVLV): face velocity 15 m/s Low velocity high volume (LVHV): face velocity 3.4 m/s 01/07/

14 Challenges with local ventilation Welding operations are characterised by frequent changes in location and welding position This makes it more difficult to control fume exposures than in fixed workplaces The effective working range of local exhausts is limited, especially with HVLV systems Correct positioning of the hood and sufficient exhaust flow rates are essential for efficient operation Work practices which include the active operation and management of the exhaust device are critical for successful outcomes 01/07/

15 General ventilation air distribution 01/07/

16 General ventilation air distribution Mixing ventilation Displacement ventilation Hybrid ventilation 01/07/

17 Mixing ventilation Air is supplied with high velocity near the ceiling which causes the air in the room to mix This results in nearly uniform temperature and contaminant concentration distributions Suitable for heating 01/07/

18 Displacement ventilation Air is supplied at slow velocity into the occupied zone Convection from heat sources creates vertical air motion into the upper zone, where the air is extracted Weak momentum operation easily deteriorated by disturbances Cool air flows near the floor Warm air rises up not suitable for heating! 01/07/

19 Hybrid ventilation Air is supplied through a displacement type diffuser assisted with a downward directed slot jet Facilitates a longer efficient operating range than with displacement ventilation Can provide a supply of warm air 01/07/

20 Hybrid ventilation 01/07/

21 Correct position of the welder relative to the supply air Supply from the front: exposure due to air flow towards the breathing zone Supply from the back: exposure due to recirculation Supply from the side: the best solution! 01/07/

22 Case study - effect of improvements on exposure Before After A welding shop was renovated by installing a new ventilation system which included heat recovery and hybrid air distribution systems. After the renovation, the workers exposure to contaminants was reduced significantly. The ímproved air quality is clearly evident in the following chart results. Chromium Chromium /07/2015 Welders urine concentration (µmol/l) 21 After Before Nickel Nickel

23 Ventilation energy consumption 01/07/

24 Energy required to heat the supply air Temperature difference, C Air density Heat capacity of air, c=1 kj/kg K Air flow rate 1 degree C temperature difference means 1.2 kw heating power for an air flow of 1 m 3 /s Average annual temperature difference in Finland is about 14 C Average heat power is thus 17 kw per 1 m3/s airflow Heat recovery from exhaust air could provide savings from 50 % up to 80 % 01/07/

25 Heat recovery energy savings 01/07/

26 Summary Welding operations need control measures to keep welders contaminant exposure below occupational limit values Local extraction can be the most performance-effective and costeffective control method Efficient control requires the proper use of the system (e.g. frequent replacement of the exhaust hood) General ventilation is needed to dilute contaminants that are not captured. Hybrid ventilation distribution offers advantages over conventional air supply methods, in that it provides clean air to the breathing zone To avoid the clogging of the heat exchanger and maintain high efficiency levels, cleaning of the exhaust air is needed 01/07/

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