Inhaling fumes should not damage your health01 March 2004

A new laboratory in a leading research institute in the UK has just been dedicated to improving the welding working environment and making it safer.

It is not that welding has suddenly become more hazardous - on the contrary, it is probably safer now to be a welder than it has ever been - but new and more stringent regulations mean that employers now have to pay much greater attention to using technologies that can combat the hazards.

In this increasingly litigious society, with its hungry 'no-win, no-fee' lawyers, no plant manager wants to be caught in a crisis like the one around asbestosis, with its vast compensation bills and subsequent greatly increased liability insurance premiums.

The Leonard Parker Pool laboratory at TWI (The Welding Institute) in Abington, Cambridgeshire was opened in March by Bevan Braithwaite, chief executive of TWI, and Air Products' European president Bernard Guerini. The laboratory has been named after the founder of Air Products, who started the company in Pennsylvania in 1940. Air Products has been working with TWI for a long time, having been the first member company with an overseas headquarters to join the then British Welding Research Association in 1964. "All manufacturing processes involve potential hazards and welding is no exception. Our key skill is our ability to do a proper job on ozone, which is difficult to remove by ventilation," says Braithwaite.

Air Products has been sponsoring the work of senior researcher Graham Carter for decades. What is different in the new laboratory, says Carter, is that he will no longer have to pack away his equipment and re-assemble it for each piece of work. Installed in the new dedicated fume laboratory, it can now be kept set up all the time, giving far greater reproducibility of results at reduced costs.

As in most areas of plant engineering and manufacturing, a risk assessment process has to be applied to fume and gas hazards from welding. Part of the solution, he says, is to "suck fumes away, but a far superior approach is to generate less fumes in the first place." Air Products has done much work on formulating shielding gases to reduce pollutants, working in conjunction with TWI. It is very evident from TWI's free publication Understanding fume and pollutant gases in welding that there can be a 5:1, 10:1 or, in one case, a 17:1 ratio between the amounts of various hazardous gases produced during similar welding operations using different shielding gas mixtures.

Noxious gases resulting from welding include carbon monoxide, nitric oxide, nitrogen dioxide and ozone, which is a particular hazard. Formed when ultraviolet radiation from an electric arc splits oxygen molecules in the surrounding air, it is a very strong oxidant that irritates the throat and airways, even at very low concentrations. The safe limit is 0.2ppm over a 15-minute time-weighted average period. This is only about double the level that can sometimes be detected outdoors on a sunny day.

Relating to fume and gas hazards in general, Carter explains, "It is difficult to assess the effect of welding process variables on human exposure because exposure measurement is poorly reproducible. Instead, researchers measure differences in fume emissions rates, the measurements of which are reproducible. Emission rate correlates with exposure - higher emission rates giving higher exposure and lower emission rates lower exposure in the same work situation. Ozone is quite difficult to measure and difficult to control as well." Unlike welding fumes, ozone is invisible.

Low levels of ozone are measured by a chemiluminescent reaction whereby the ozone reacts with another chemical to produce a very small amount of light.

Particulate fumes from welding are initially only 0.01 to 0.1µm across at source. By the time they reach the welder's breathing zone, they have mostly agglomerated to 1 to 2µm across. The largest particles (wider than 5 µm) are deposited in the upper respiratory tract. The smallest (below 0.1µm) are mostly breathed in and out again. However, particles in the size range 0.1-5µm penetrate the alveoli in the innermost parts of the lungs and stay there. Plant Engineer has been shown filter papers thickly covered with fume particles derived from a single welding session. Filter papers placed on sampling intakes inside a welder's helmet had also received a substantial coating from single sessions.

It is no surprise, therefore, to discover that regulations on exposure to fume are becoming stricter. Carter says that there is now great concern about exposure to chromium and manganese compounds in fume derived from welding wires and electrodes. The American Conference of Governmental Industrial Hygienists (ACGIH) is said to want to drastically reduce safe limits for exposure to manganese, following a court case in the USA. Graham Carter says, "I don't even think that OSHA [the US Occupational Safety and Health Administration] will accept the ACGIH limit value but ACGIH values are often used in court because they are purely health based. Most limit values take other factors (socio-economic) into account."

The ultimate solution to possible problems caused by inhaled weld fume could be to use robots to undertake welding.

TWI has been a participant in a European Community project aimed at developing technology for the welding of large steel fabrications using autonomous robots. The project is known as NOMAD and uses a six-axis robot arm mounted on an autonomous robot transport vehicle (RTV) that allows the robot to be brought to the part. The structure to be welded is placed above floor level on a platform so that when the RTV moves around the structure, the robot arm can access all the joints to be welded.

The approach allows for all parts to be tack welded and robot welded in the same location, hopefully reducing the need to transport large structures between workstations. Equipment carried on the RTV includes welding power source, shielding gas, welding consumables and ancillary equipment. The project, designated EC G1RD-2000- 00461, is due to be completed in August.

Technical pointers
- Generating less fume, rather than extracting it, is the preferred solution

- Rates of emission tend to be measured rather than rates of human exposure, as the latter is poorly reproducible

- Noxious gases resulting from welding include carbon monoxide, nitric oxide, nitrogen dioxide and ozone, which is a particular hazard

- Regulatory bodies are concerned about exposure to chromium and manganese compounds

SOE

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