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Control of fume arising from electric arc welding of stainless steels

OC 668/29

This 2-part OC, which revises and replaces OC 668/28, gives advice on the control of fume arising from electric arc welding processes. Attention is drawn to an exposure matrix which can be used to identify the type of ventilation required. The attached Information Document (ID) may be copied to interested persons outside HSE. Revised information is contained in OC paras 11,12,16-27 and ID paras 4,9,54-55.

Introduction

1 The majority of welding processes release fume which has to be controlled. The fume arising from stainless steel welding has the additional hazard of containing harmful metal compounds. This document advises on how exposure to this fume may be controlled. It is restricted to fume arising from the manual metal arc (MMA), flux cored arc (FCA), metal inert gas (MIG) and tungsten inert gas (TIG) welding processes. An exposure matrix is provided in the ID appendix as an easy to use guide for employers and inspectors, as to the type of ventilation required.

2 Welding also generates ozone, particularly when using TIG or MIG welding processes. Ozone is a respiratory irritant and is assigned an occupational exposure standard (OES). However, the assessment and control of exposure to ozone are not covered by this document. Inspectors are instead referred to Guidance Note EH 38 (Rev) Ozone: Health hazards and precautionary measures (file 285). Also, welding in a confined space is not covered by this document. Inspectors should instead refer to Asphxiation hazards in welding and allied processes.

Stainless steels

3 There are various types of stainless steel available. These can be categorised according to their metallurgical composition, eg in terms of their nickel and chromium content (the metallurgical composition of the steel is not however directly reflected in the composition of the fume released during welding). Those types which are commonly welded include ferritic stainless steels, austenitic stainless steels and duplex stainless steels. Inspectors should be aware when components or alloys are so described, it is stainless steels which are being referred to.

4 Metal fabricators are unlikely to weld solely stainless steels, as a result inspectors may not see stainless steel welding actually taking place. They should therefore enquire into the type of metals which are welded. If a company has welding approval for stainless steel welding this is a good indicator that they will be likely at some time or another, to undertake this type of welding.

Welding fume

5 Stainless steel welding fume may contain several substances assigned maximum exposure limits (MEL). The most important of these are likely to be chromium (VI) and nickel. Control of these substances to the lowest level reasonably practicable is required (see ID paras 21-22).

6 Detailed guidance on the assessment of fume from the welding of stainless steels is contained in GN EH 54 Assessment of exposure to fume from welding and allied processes(file 668). Information on the composition of the welding fume can be obtained from the consumable material safety data sheet. Welding Information Sheet No 1 details the type of information that should be supplied. This information can be used as is described in GN EH 54 to calculate an overall control limit for that particular fume (see also ID para 30).

Control of exposure to welding fume

7 Exposure to stainless steel welding fume can be controlled by using a hierarchy of measures. The priority is to reduce the quantity of fume generated (see ID para 36). This should be achieved where possible by substituting low fume processes for higher fume processes (see paras 10-13 and OC 273/14 COSHH and substitution), followed by improvements in working practices (see ID paras 46-47).

8 Only when the quantity of fume generated is as low as is reasonably practicable should ventilation be used to ensure exposure to any residual fume is adequately controlled. The ventilation control approach selected may consist of using either natural ventilation, mechanical ventilation, local exhaust ventilation (LEV) or a combination of all 3. The exposure matrix (see ID appendix) may aid the selection process. In general however, if prevention or reduction of exposure to insignificant levels is not achievable by alterations to the welding process or working conditions, it is likely LEV will be required.

9 Further guidance on the control of exposure is provided by GN Note EH 55 The control of exposure to fume from welding, brazing and similar processes (file 668).

Welding processes

10 The choice of welding process can significantly affect both the quantity and composition of fume emitted. Enquiries should therefore be made into the type of welding processes used. The 4 most common arc welding processes are:

1) Manual metal arc (MMA) - an arc is formed between the parent metal to be welded and a metal rod (the electrode), the end of which melts in the heat of the arc. The molten metal particles are carried by the arc stream into the molten pool of parent metal at the other end of the arc, forming the filler metal of the weld. The rod has a flux coating which melts simultaneously forming gas and slag (a non-metallic residue) which protects the weld pool from the surrounding atmosphere. This process is often referred to as stick welding.

2) Gas shielded metal arc (MIG/MAG) - an arc is formed between the parent metal to be welded and a metal electrode, in the form of a solid wire. The wire is fed at a steady rate through the centre of a welding gun which is often hand held. A steady stream of gas flows around the metal electrode to protect the parent and molten weld metal from oxidising. The welding wire is of a relatively small diameter. There are numerous mixes of shielding gases on the market. Each, in addition to its role as a shield, has its own particular specialist purpose. The choice of gas should be left to competent persons.

3) Flux cored arc (FCA) - as with MIG/MAG welding an arc is formed between the parent metal to be welded and a metal electrode, in the form of a wire which is continuously fed. The same welding equipment is also used. With self-shielded FCA welding the wire's core contains powdered metal and gas forming compounds. It is normally used outdoors or in other drafty situations. Gas-shielded wires require an additional shield to protect the weld pool and are only used indoors. In principle the flux core of the wires contains similar components as those in the flux covering of a corresponding MMA electrode.

4) Tungsten inert gas (TIG) - an arc is formed between the parent metal to be welded and a metal electrode made from tungsten, which does not melt. The joint may be made by melting the parent metal - autogenous welding (running in) or from a filler rod melted into the joint.

11 Further information on the arc welding processes including help in identifying each process can be obtained from The Welding Institute's (TWI) Website at www.twi.co.uk (click on Information and know-how, followed by JoinIT Technical Information, followed by Knowledge summaries, followed by Joining technologies and lastly Arc welding).

12 Of the four welding processes MMA/FCA welding generate the greatest quantity of total fume. The hexavalent chromium content of the fume is high compared to that released by MIG and TIG welding. The nickel content is however lower than with MIG welding. TIG welding generates very low levels of total fume. The nickel and hexavalent chromium content of the fume is also very low.

13 The use of TIG welding should be suggested as an alternative to the other arc welding processes detailed. However, inspectors should be aware there may be practical difficulties in substituting one welding process for another. They should satisfy themselves that the employer has as a minimum, given active consideration to doing so. However, MIG or TIG welding in a confined or semi-confined space should not be recommended due to the potential for a build up of shielding gases leading to the risk of asphyxiation (see OC 288/6 (Rev)).

14 The welder's exposure to fume from electric arc welding of stainless steel is unlikely to be adequately controlled without the use of specific measures unless:

1) the method used is a low fume producer such as TIG; and

2) the process is conducted under good working conditions; and

3) only for short periods.

Action by inspectors

15 Where inspectors encounter stainless steel welding they should ensure the measures set out in the ID are adopted. Particular attention should be paid to the following key issues:

1) a suitable and sufficient COSHH assessment has been completed for each type of welding process used, which assesses the risks from both total welding fume and its constituent components (ID paras 23-33);

2) the control measures selected have been chosen according to the COSHH hierarchy, emphasis having been placed on substitution and improved working practices (ID paras 38-47);

3) for each welding process undertaken the ventilation used is capable of achieving the required level of fume control ([ID paras 48-52 and ID appendix),

4) although in the case of MMA and FCA welding LEV is probably necessary; where LEV is provided training has been given in its correct use (ID para 50);

5) where respiratory protective equipment (RPE) has been provided it has not been selected in preference to other control measures such as ventilation, which would be reasonably practicable to adopt. The RPE should fit the wearer correctly (may be achieved by qualitative and quantitative face fit tests), be suitable for the work and provide adequate protection. Welders should be trained and supervised in its correct use (ID para 53); and

6) the appropriate level of health surveillance is provided (ID paras 54-57). Where it is identified that health surveillance is required, baseline questionnaires should be conducted as a minimum. The advice of a specialist group medical inspector should be sought prior to enforcing a higher level of surveillance.

Enforcement

16 The following is a guide to when enforcement action may be appropriate. It is based on the Enforcement Management Model (EMM) Operational version 2.0, and the document EMM: guidance on application to health risks(available on the Intranet). Any action taken should reflect any subsequent changes to EMM. The final decision on enforcement action should also take account of local factors.

Immediacy of risk

17 Research suggests that stainless steel welders (and welders in general) exhibit an elevated incidence of lung cancer. Constituents of the fume, in particular chromium (VI) and nickel, also have the potential to cause occupational asthma. A possible risk of a serious health effect will exist where the MEL for either chromium (VI) or nickel is exceeded. Evidence to support such an opinion will exist where:

1) there is evidence of high fume levels, ie as generated by MMA and FCA welding and MIG welding using spray transfer mode; and

2) there are either no control measures in use, eg no RPE or LEV; or

3) the control measures used are ineffective. In the case of LEV this could arise for example if it is incorrectly designed; missing a capture hood; wrongly positioned, and/or not properly maintained. Even if suitable the RPE could either be incorrectly worn, have the wrong filters, be in need of repair or maintenance or have undergone unsuitable modifications.

18 In such situations, inspectors should consider issuing a prohibition notice (PN) as discussed in EMM Section 2. However, in cases where LEV is either not used or is ineffective but RPE is worn in line with the conditions detailed below, the likelihood of a person developing either lung cancer or asthma will be remote. As it is not anticipated that a serious health effect will occur issuing a PN in such circumstances may not be appropriate. For this to be the case however the RPE has to be:

1) suitable (including its filters) and provide adequate protection;

2) correctly worn;

3) subject to a qualitative face fit test to ensure a good face seal is obtained (face seal RPE only);

4) regularly maintained in accordance with a maintenance programme; and

5) correctly stored when not in use.

19 Suitable training in using and maintaining the RPE should also have been provided which is backed up with adequate supervision. Where RPE is worn which satisfies these conditions risk gap analysis should be used to identify the appropriate enforcement action to take to address the remaining areas of concern.

20 If welding in a confined space is encountered see OC 288/6 (Rev) for appropriate enforcement action.

Benchmark standards

21 The benchmark set should be considered as a nil/neglible risk of a serious health effect. This will be achieved where exposure to chromium (VI) and nickel has been reduced to as far below their respective MELs as is reasonably practicable. Where possible this should be achieved by a package of measures including substituting a low fume emitting process for a high fume process, improved working practices (ie welding with the head out of the fume, using a lower serviceable weld), LEV and lastly RPE. Adequate training and supervision should also be provided.

Risk gap

22 The risk gap as derived from EMM table 2.1 for two key scenarios are summarised below. Inspectors may use the scenarios as a guide to making their assessment of actual risk, and the subsequent risk gap. However, inspectors must ensure that they base their assessment of risk on the factors they find at site.

Scenario Actual risk Risk gap
There is evidence of high fume levels as generated by MMA and FCA welding (see OC para 12) - engineering controls are not present although RPE is in use which fulfils the requirements detailed in OC para 18 . Remote risk of a serious health effect. Substantial
A high fume emitting process is in use (see OC para 12) - suitable LEV and RPE are in use which are achieving an acceptable level of control. Training has not however been provided in their use. Remote risk of a serious health effect. Substantial

Initial enforcement expectation (IEE)

23 The following are relevant to deriving the authority of standards for use in EMM table 5.1 and hence for deciding the IEE.

Title Authority
HSE Booklet L5 (third edition 3/99)General COSHH ACOP and Carcinogens ACOP and Biological ACOP Control of Substances Hazardous to Health Regulations 1999 Defined
GN EH 54 Assessment of exposure to fume from welding and allied processes Interpretative
GN EH 55 The Control of exposure to fume from welding, brazing and similar processes Interpretative
HSE Booklet HSG 204 Health and safety in arc welding Interpretative

24 The EMM considers COSHH assessment as an administrative measure. The standard for COSHH assessment is a defined standard, being found in the Control of Substances Hazardous to Health Regulations 1999. Any absence, or inadequacies with an assessment should be considered using EMM table 5.2.

Strategic factors

25 Inspectors are asked to bear in mind that the control of exposure to stainless steel welding fumes is the subject of a current Sector Objective which aims to secure compliance by employers with COSHH and in particular the MELs for chromium (VI) and nickel. Failure to consistently issue improvement notices for the scenarios in the table in para 22 may have a negative impact upon employers attitudes. This should be considered as a strategic factor for the purposes of EMM table 7.

Compliance issues

26 Where a PN is issued compliance with the notice may be achieved in the short term by providing the welder with adequate RPE, and segregating other people exposed to the fume from the source of exposure. If others exposed cannot be transferred elsewhere short-term compliance may be achieved by providing them with adequate RPE. To be adequate the RPE has to satisfy the conditions detailed in para 18. Such action is only acceptable until alternative means of control of exposure can be established, ie LEV.

27 Where a notice is issued requiring LEV to be provided, the notice's schedule should instruct the employer to prove upon its installation that the LEV is capable of achieving the required level of control. The employer should demonstrate this by arranging for employee exposure to stainless steel welding fumes to be monitored whilst the LEV is in use. To ensure the effectiveness of the LEV is not adversely affected by incorrect use the employer should also be required to provide training in its correct use.

Cancellation of instructions

28 OC 668/28 - cancel and destroy .

Date first issued: 6 July 2001
(220/FOD/1028/2001)
Ref: J:\Editors\intranet\ocfiles\600_699\668_29.lwp

Updated 2014-01-31