Employees in the fabrication industry face potential exposure to a range of hazardous substances on a daily basis. Some of these hazards are well known and understood; some are only just beginning to be properly understood despite the fact that the basic processes involved have been unchanged for many years.
Weld Fume Inhalation
A key change recently has been the identification of weld fume as a potential carcinogen. In 2018, the International Agency for Research on Cancer (IARC) published a document (monograph 118) detailing that welding fumes, and UV radiation from welding, are Group 1 carcinogens. Exposure to weld fume has been shown to positively correlate with increased rates of lung and potentially also kidney cancer in humans; previously the link was suspected but not adequately proven.
On release of this paper, the UK HSE changed their advice on exposure to weld fume. They have made clear that LEV must be in place for all indoor welding operations and suitable RPE for outdoor welding. They have also stated that they will not accept any level of exposure to weld fume; ie, duration of exposure is irrelevant. The standard hierarchy of control applies – Elimination, Substitution, Controls, PPE.
Of course, the existing known hazards must still be accounted for; these may include metal fume fever, stomach ulcers, kidney damage and nervous system damage, dependant on type of fume.
As a manufacturer of Local Exhaust Ventilation equipment, we have a role at level 3 of this hierarchy; reducing the risk using engineering controls. In the UK, we have no mandatory standard for weld fume extraction equipment; however ISO15012 provides guidance which may or may not be adopted.
While not as hazardous as inhalation of weld fume, long-term exposure to inhalation of grinding dust can lead to reduced lung function; occupational asthma; inflammation and damage to soft tissue in the respiratory system. Of greater concern are alloyed materials as they can contain potential carcinogens; while exotic metals such as tungsten, chromium, etc are known in some cases to lead to an increased risk of cancer. Skin sensitisation is possible when working some metals.
LEV design must not only take account of the nature and hazard level of the dusts; but also of the presence of potential hot material from grinding processes; and the combination of different materials in the collected dust.
Fire and Explosion Risk
The explosive nature of many dusts is well documented and understood in industry. Aluminium is often found to be the cause of major explosions in fabrication plants; although this is now a relatively rare occurrence due to increased understanding of the hazards posed by finely divided particulate. In many cases, explosion risk can be a good example of ‘a little knowledge is a dangerous thing’; it is essential, if you believe you have a potential explosion risk, to contact an experienced professional who can quantify the risk for you.
It is not uncommon, as a supplier of LEV systems, to be asked to supply ‘ATEX rated’ equipment by a user who has not correctly identified which zone they are working in; the extent of the zone; or the impact of other equipment located in the potential risk area. This opens managers to a range of risks aside from the potential for danger; for example, installation of one item of ATEX rated equipment implies an understanding of an explosion risk; allowing non-rated equipment into the same area suggests disregard for that risk unless the reasoning behind this is documented and understood.
Equally, consideration should be given to fire risk; titanium dust, even without being raised into a suspended cloud which could enable an explosion, is flammable; and tends to produce sparks when worked. Titanium dusts must be collected in a wet filter system except in very specific circumstances.
While we are becoming more aware of the risks of inhalation of metal dusts and fumes, and of the explosion risk a wide range of common dusts can introduce, many people are unaware of the potential fire or explosion risk created by some metals, or combinations of metals. Aluminium dust is known to be highly explosive in finely divided form and explosions in aluminium handling plants are surprisingly common.
However, even with proper explosion protection mechanisms, the risk of fire created by combining metals in a single dust extraction system is little known. In particular, aluminium and steel dust, when combined in the correct proportions, can create thermite; simply leaving finely divided steel and aluminium dust together over time can lead to a fire as the mixture can self-ignite. In simple terms, steel dust can corrode into ferrous oxide; and ferrous oxide mixed with aluminium creates thermite. This mixture usually requires a heat source to ignite it but can self-combust in certain circumstances. For this reason, we always specify that metals should not be mixed in a dust collector.
In short, get advice, and “know what you don’t know”. A sensible, pragmatic advisor who knows the risks in detail can more than pay for themselves. Ask a professional when specifying dust extraction systems; if you believe you have a health hazard talk to an Occupational Health professional and for a potential dust explosion risk, obtain further advise from an ATEX qualified person.