Hazardous materials: asbestos, refractory, silica and chemicals

Not every hazard on an outage acts quickly. A fall or a gas release injures in seconds; the dust and fibres a boilermaker breathes while chipping refractory or cutting through old insulation may cause disease thirty years later. Kiera's grandfather was a pipefitter, and he died of mesothelioma, a cancer caused by asbestos he breathed in plants in the 1960s. When Imran's orientation reaches the health hazards, she is the one asking the questions. This lesson covers the materials boilermakers are most likely to meet: asbestos, refractory and its fibres, crystalline silica, ash and dusts, welding fume, and the chemicals of power plants, refineries and mills, with the controls that keep exposures down.

Knowing what you are working with

Workers have the right to know the hazards of the materials they work with. In Canada that right is delivered through WHMIS, the Workplace Hazardous Materials Information System, which since 2015 has followed the international Globally Harmonized System. Suppliers label hazardous products with pictograms, signal words and hazard statements, and provide a safety data sheet, an SDS, with sixteen standard sections covering hazards, composition, first aid, firefighting, handling, exposure controls and protective equipment. The employer must make the SDSs available, label products decanted on site and train workers to understand both. The federal regulations were updated in 2022 to align with a newer revision of the international system.

Some of the most important hazards have no label at all, because they are not products bought from a supplier. The asbestos in a 1970s boiler, the silica dust released when old refractory is broken out, the lead in old paint and the fume from a weld are all created or uncovered by the work. For these, the owner's records, sampling and the contractor's hazard assessment are what tell the crew what they face.

Asbestos

Asbestos is a group of natural mineral fibres that were used for decades in boiler insulation, pipe lagging, gaskets, rope packing, refractory, cement board and fire-resistant cloth because they resist heat and do not burn. When asbestos-containing material is disturbed, it releases fibres fine enough to reach deep into the lungs, where they stay. They cause asbestosis, a scarring of the lungs; lung cancer; and mesothelioma, a cancer of the lining of the chest or abdomen that is almost always caused by asbestos. These diseases appear decades after the exposure, and there is no known safe level.

Most plants built before about 1990 still contain some asbestos. Owners are required to know where it is, and a plant like Riverbend has an asbestos inventory showing which insulation, gaskets and refractories contain it. Removing asbestos is specialized work done by trained abatement contractors under strict controls, and in Alberta it is governed by the OHS Code's asbestos requirements, with an occupational exposure limit of 0.1 fibres per cubic centimetre averaged over eight hours. Boilermakers do not remove asbestos unless they are trained and the work is planned as abatement.

The rule for Kiera is simple: if she finds material she suspects might contain asbestos, insulation with no label, an old gasket, a crumbling grey rope, she stops, does not disturb it further, keeps others away and reports it to her foreman. The material is sampled and tested before work resumes. This happens on almost every outage at older plants, usually when a crew opens a casing panel or a flange that the inventory missed.

Refractory and its fibres

Refractory is the heat-resistant lining of furnaces, burner throats, ducts, cyclones and coker drum skirts. It comes as firebrick, castables poured like concrete, plastic refractories rammed into place, and ceramic fibre blankets and boards. Boilermakers often break out old refractory to reach tubes and anchors, and install new refractory anchors before the refractory crew pours.

Refractory ceramic fibres, used in high-temperature insulation blankets, are a respiratory hazard in their own right and are classed as a possible human carcinogen. After long service at high temperature, some of the fibre changes to cristobalite, a form of crystalline silica, which makes the old blanket more hazardous to remove than the new blanket was to install. Castables and firebrick contain silica too, and chipping them out with a pneumatic hammer releases clouds of fine dust. On the Unit 2 burner throats, the refractory demolition is done wet, with local exhaust and respirators, and the debris is bagged rather than swept.

Crystalline silica and ash

Crystalline silica, mostly in the form of quartz, is in sand, concrete, many refractories, abrasive blasting media and the ash of many fuels. Breathing fine respirable silica dust causes silicosis, an incurable scarring of the lungs, and increases the risk of lung cancer, kidney disease and other illnesses. Alberta's occupational exposure limit for respirable crystalline silica as quartz is 0.025 mg/m³ averaged over eight hours, one of the lowest limits for any dust.

Boiler ash adds metals to the mix. Ash from coal contains silica and trace metals; ash from oil firing contains vanadium and nickel compounds, which are toxic; and ash in the back pass of any boiler can be hot, caustic when wet and very fine. Riverbend burned coal for forty years before its conversion, and there is still old fly ash packed into corners of the economizer and the ash hoppers. Cleaning it out is done with vacuum trucks and wet methods, never by blowing it out with compressed air, which puts it into the air for everyone nearby.

Welding fume and metals

Welding and cutting produce fume, a cloud of fine metal oxide particles condensed from vaporized metal, and gases such as ozone, nitrogen oxides and carbon monoxide. Manganese in steel fume can cause nervous system damage with long exposure. Welding or cutting stainless steel and high-alloy tubes, common in superheaters, produces hexavalent chromium, a lung carcinogen with a very low exposure limit. Cutting or heating steel coated with old lead paint releases lead fume. Galvanized steel releases zinc oxide fume, which causes metal fume fever, a short flu-like illness. Fume is controlled by local exhaust ventilation at the arc, by positioning the head out of the plume, by general ventilation in enclosed spaces and by respirators where those are not enough. The welding courses later in the program cover fume control in detail.

Chemicals

Each kind of plant has its own chemicals. Power boilers are chemically cleaned from time to time with acid solutions that dissolve scale; the acid can release hydrogen, which is flammable, and the spent solution is corrosive. Boiler water treatment uses amines, phosphates and oxygen scavengers. Refineries and upgraders have hydrogen sulphide, benzene and other aromatic hydrocarbons, caustic, sulphuric acid and, in some units, hydrofluoric acid, which needs special protection and first aid. Pulp mills have caustic and sulphide-rich liquors, and chlorine dioxide in the bleach plant. Opening equipment that held any of these brings the risk of contact with residues, and the line-break permit that the owner issues before a flange is opened lists the chemical, the PPE and the first aid.

Benzene illustrates how low some limits are. It causes leukemia with long exposure, and the limits for it are measured in fractions of a part per million. Before Kiera's crew opens an exchanger in benzene-bearing service at Northgate, the owner's industrial hygienist checks the atmosphere with a PID and, where needed, the crew wears supplied-air respirators for the opening.

Controlling exposures

The hierarchy of controls applies to health hazards exactly as to any other. Elimination and substitution come first: replacing asbestos gaskets with non-asbestos ones, using cold cutting rather than torch cutting on painted steel, choosing a low-silica refractory. Engineering controls come next: wet methods that keep dust out of the air, local exhaust ventilation and dust collectors, enclosures around demolition work, HEPA vacuums instead of brooms and compressed air. Administrative controls include limiting the time and number of workers in a dusty area, scheduling dusty work when fewer people are nearby, hygiene facilities and decontamination, and training. Respirators come last.

When respirators are needed, they must be the right type for the hazard and properly fitted. A filtering respirator with P100 or HEPA filters protects against dusts and fibres, but not against gases or low oxygen. A supplied-air respirator brings clean air from outside. Each worker who wears a tight-fitting respirator is fit tested for the model and size they use, at least once a year, and checks the seal each time they put it on. Facial hair under the seal defeats the fit. In Canada, respirator selection, use and fit testing follow CSA Z94.4, which Alberta's Code refers to.

Exposure is checked by sampling. An industrial hygienist puts a small pump and filter cassette on a worker's collar, in their breathing zone, for the shift, and the lab measures how much of the contaminant was collected. The result is a time-weighted average over the eight hours, compared with the exposure limit. The code below works out an eight-hour average from several shorter samples taken during a refractory demolition shift, and compares it with the limit. When a worker is exposed to several substances that affect the same organ, the fractions of each limit are added, and the sum must stay below one.

# Eight-hour time-weighted average for respirable silica from task samples (illustrative)
limit = 0.025        # Alberta OEL, respirable crystalline silica (quartz), mg/m3
samples = [  # task, hours, concentration in the breathing zone (mg/m3)
    ("refractory demolition, wet + exhaust", 2.0, 0.090),
    ("bagging debris",                        1.5, 0.030),
    ("anchor welding",                        3.0, 0.004),
    ("breaks, change room",                   1.5, 0.000),
]
total_h = sum(h for _, h, _ in samples)
twa = sum(h * c for _, h, c in samples) / 8.0
print(f"hours sampled: {total_h}")
print(f"8-hour TWA: {twa:.4f} mg/m3, {100 * twa / limit:.0f} % of the limit")
# a respirator with an assigned protection factor reduces what the worker breathes
for name, apf in (("half-face P100", 10), ("powered air-purifying, loose hood", 25)):
    print(f"inside a {name} (APF {apf}): {twa / apf:.4f} mg/m3, {100 * twa / apf / limit:.0f} % of the limit")
# mixed exposure: fractions of each limit that affect the lungs add together
fractions = {"silica": twa / limit, "refractory fibre": 0.30}
print(f"combined lung exposure index without respirator: {sum(fractions.values()):.2f} (must be below 1)")

hours sampled: 8.0
8-hour TWA: 0.0296 mg/m3, 118 % of the limit
inside a half-face P100 (APF 10): 0.0030 mg/m3, 12 % of the limit
inside a powered air-purifying, loose hood (APF 25): 0.0012 mg/m3, 5 % of the limit
combined lung exposure index without respirator: 1.48 (must be below 1)

The answer shows why the controls are layered. Even with wet methods and local exhaust, the shift's average is over the limit, almost all of it from the two hours of demolition, and the respirator brings what the worker actually breathes well below it. The combined index for silica and fibre is a reminder that limits for separate substances are not separate allowances. And the samples guide the next improvement: the largest share of the dose comes from demolition, so that is where better exhaust or a longer-reach tool would do the most good.