- The common hazardous gases are carbon monoxide, oxygen, hydrogen sulfide, nitrogen oxides, methane, and chlorine dioxide.
- Poorly ventilated areas and confined spaces are particularly dangerous in the industry due to gas accumulation.
- Various processes, such as welding, cutting, earthworks, painting, transporting, woodwork, insulation installation, and equipment use, are the primary sources of hazardous gas emissions.
- Building and cleaning materials can be associated with hazardous gas exposure.
According to the International Labour Organization, construction workers’ deaths due to occupational accidents are three to four times higher than in other industries. Around 108 thousand worker fatalities occur on-site, accounting for 30% of total occupational fatal injuries. One of the foremost risks is exposure to dangerous substances, including gases. Therefore, industrial hygienists and safety managers need to be aware of the dangers and risks that workers face, as most accidents are preventable, in order to make workplaces safer for them.
Why Construction is So Hazardous
The Health and Safety Executive in the UK, which regulates workplace safety, has identified several reasons for the disproportionately higher number of occupational accidents in the construction industry:
Varied work environments: The construction sector is one of the largest in the world, encompassing a range of industries, including building, demolition, civil engineering, and maintenance. Different types of work, often outdoors, unlike in controlled factory settings, can be challenging. The types of work can vary in a single site and expose workers to new risks. So, the number of hazards to which workers are exposed is numerous, including dust, gases, asbestos, work positions, and noise, among others.
Time lag in symptoms: The serious health effects of some chemical exposures can take time to manifest, and if the immediate impact is not significant, the role of harmful substances may not be considered.
Type of employment: Many workers in the construction sector work in small companies, are self-employed, or frequently change employers, which can result in them not receiving the required medical attention or maintaining accurate records of exposure.
The places where workers in the construction sector are exposed to hazardous gases include confined space entry, trenching, shoring, welding, cutting, transporting, terracing, woodwork, painting, insulation installation, and gas leaks from equipment such as fossil fuel generators, as well as storage spaces.
Occupation Risks in the Construction Industry
The construction industry accounts for 40% of work-related cancers, more than any other industry. The construction industry sees around 3700 deaths annually due to cancer. Asbestos (70%) is the leading cause, followed by silica (17%), paints and diesel fumes (6-7% each). The deaths of workers on construction sites in developing countries are higher than global averages and can be 3 to 6 times greater than in other industries.
As in all industries, illness causes more absenteeism than injuries. However, fires and explosions caused by flammable gases can result in significant damage and injuries.
Among the chemicals to which workers are exposed, dust, fumes, vapors, and gases emitted during construction processes account for a significant proportion of damage. Workers are at risk from gases through inhalation and skin contact, which can lead to respiratory and lung diseases, as well as skin problems. Hazardous gases and vapors can accumulate on eating and drinking utensils when kept in proximity to workplaces, allowing people to ingest and inhale these gases.
- Dust: Construction dust is produced from materials such as asbestos, silica, wood, and also includes general dust from gypsum, limestone, marble, and plasterboard. Fine dust (PM2.5 and PM10) is a serious health risk. These can lead to severe respiratory and cardiac problems and premature death.
- Fumes and vapors: The fumes produced from solids during processes are beryllium, iron oxide, mercury, zinc, lead, and cadmium. Materials used in the construction industry that produce hazardous fumes and vapors include solvents, paints, glues, chlorinated pesticides (such as lindane), resins, pigments, and binders.
- Gases: The gases can be toxic, flammable, corrosive, asphyxiant, or inert.
The dangers from gases, dust, and fumes are present in both chronic and acute exposure. Chronic exposure to low concentrations of toxic gases can cause lung damage and cancer.
The common hazardous gases encountered in the construction sector are listed next.
The Hazardous Gases in the Construction Industry
While the exact gases present at a work site depend on the specific tasks being undertaken, some hazardous gases associated with everyday tasks in construction are discussed below.
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Oxygen
Air has 20.9% oxygen (O2). When the level of the gas is lowered to 19.5% and below, the deficiency can cause dizziness and, in extreme cases, death. On the other hand, oxygen accumulation that increases its level to 23.5% and above increases flammability and can be fatal. Such conditions arise in confined spaces when the production of other gases during the work process accumulates and displaces oxygen.
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Carbon Monoxide
In construction sites, carbon monoxide (CO) is the leading cause of fatal gas poisoning. The incomplete combustion of fossil fuels generates CO, as in gas-powered generators. Welding can produce CO due to the breakdown of carbon dioxide used as the inert shielding gas, especially in areas with poor ventilation. The gas accumulates in areas with poor ventilation, like confined spaces, making people unconscious and confused with fatal consequences. The gas is colorless and odorless, making manual detection challenging.
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Hydrogen Sulfide
Hydrogen sulfide (H2S) is a toxic and flammable gas produced by the decay of degradable matter, such as in waste tanks and pits. It is also found in brownfield sites where waste has accumulated. Demolition can release H2S from historically unknown sources. People working in foundations, tunnels, trenches, shafts, and storage units can also be exposed to accumulated hydrogen sulfide. This is also a gas that people can find in confined spaces due to accumulation.
At lower concentrations, it can be detected by its characteristic rotten egg smell; however, at levels (100 ppm or parts per million) where even acute exposure can be poisonous or immediately fatal, the gas numbs the olfactory functions in people, creating a false sense of security.
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Ozone
Ground-level ozone (O3) is produced during welding and cutting operations. The ultraviolet light in the welding arc and oxy-acetylene welding produces ozone. The gas is generated by gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and plasma arc cutting. O3 is a highly reactive gas that attacks all mucous membranes, causing lung damage. It can also destroy equipment.
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Methane
Methane is produced through microbial activities and is often encountered during trenching, as it is a heavy gas that tends to settle to the bottom. It can also be released during demolition from unknown sources and in brownfield sites. Methane is also released by demolition waste that is reused for construction. Methane can be trapped underground and is released during earthworks and excavation. Hence, methane is encountered while working in foundations, tunnels, shafts, trenches, and storage units.
Methane is dangerous because it is highly flammable and is an explosion risk.
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Nitrogen
Nitrogen (N) is released during construction due to the use of equipment. The gas emission is so concerning that in Amsterdam, where construction accounts for 0.6% of the nitrogen emissions, the Dutch are imposing strict regulations on the number of constructions that can be undertaken to control the harmful emissions. Nitrogen is also released during the construction due to the use of equipment and combustion systems.
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Nitrogen Oxides
The nitrogen oxides (NOx) found at construction sites are nitric oxide (NO) and nitrous oxide (N20). The two nitrogen oxides are produced from nitrogen and oxygen in the air that combine during welding and cutting, as well as during the combustion of fossil fuels. NO quickly converts to NO2, which is the gas that is a health concern. High concentrations of the poisonous gases can cause shortness of breath, chest pain, and pulmonary edema. NO2 is also an air pollutant.
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Volatile Organic Compounds
Volatile Organic Compounds (VOCs) are found in many materials used by the construction sector, which emit these as gases. The VOCs can be present as liquids or solids. Common materials that contain VOCs include paint, adhesives, building partitions, plywood, and binders. The most common VOC is formaldehyde, which is a binder for insulation materials and an adhesive for wood panels. Other VOCs are phenol and acetaldehyde. The VOCs are toxic and can cause headaches, nausea, asthma, cancer, and death. VOCs can also cause asphyxiation in confined/poorly ventilated spaces and explosions.
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Phosgene
Chlorinated hydrocarbon solvents are used for cleaning and degreasing operations on construction sites. The chlorinated hydrocarbons present near welding sites are broken down by the ultraviolet light used in the process, which can produce phosgene. It reacts with water in the lungs to produce hydrochloric acid, which damages the tissues.
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Chlorine Dioxide
The construction industry is a major user of chlorine dioxide (ClO2). The yellowish-green gas is used for disinfection because of its antiviral and antimicrobial properties. Since many workers use the same equipment, scaffolding, and tools, chlorine dioxide is used for disinfection. It improves sanitation in the workplace to protect workers’ health and also removes strong odors from materials, waste, and machinery, thereby enhancing air quality. Constructions for food processing are also fumigated with ClO2 gas before people start using the building.
ClO2 exposure occurs due to poor installation and maintenance of equipment for dispensing the gas, as well as leaks and accidental spills in the construction industry. ClO2 is a toxic, corrosive, and explosive gas that is unhealthy, a fire risk, and can damage infrastructure and equipment.
Monitoring The Hazardous Gases
In most cases, the increase in gases is the problem, and monitoring the air through gas detectors can alert workers to take necessary precautions, such as leaving the area or implementing other remedial measures. Portable gas analyzers and vacuum pumps are required equipment that workers must have to enter confined spaces. Fixed gas analyzers in poorly ventilated areas can continuously monitor the air and alert people to any increase above permitted levels established for each gas. Interscan produces both portable and fixed gas analyzers for over twenty hazardous gases, including most found in the construction industry.
Safety managers and industrial hygienists can schedule a consultation with Interscan to learn more about the gas analyzers that can help keep your staff and equipment safe.
FAQ
Sources
Acharya, A., Gokhale, V.A., & Shirolkar, M. (2016). Occupational Risk in Construction Sites With Reference To Chemical Hazards. IOSR Journal of Applied Chemistry, 9(11): 2278-5736. DOI: 10.9790/5736-0904023742
HSE. (n.d.). Construction health risks: Key points. Retrieved from https://www.hse.gov.uk/construction/healthrisks/key-points.htm
HSE. (n.d.). Construction Information Sheet No 36 (Revision 3). Retrieved from https://www.hse.gov.uk/pubns/cis36.pdf
ILO. (2015, March 23). Construction: a hazardous work. Retrieved from https://www.ilo.org/resource/construction-hazardous-work
Rogers, D. (2025, April 23). Hundreds of Dutch power projects at risk over nitrogen confusion. Retrieved from https://www.globalconstructionreview.com/hundreds-of-dutch-power-projects-at-risk-over-nitrogen-confusion/
