Construction Hazards what you don’t see will hurt you - David D. Wagner

Every day, people drive down highways and streets looking at the towering cranes and scaffoldings on construction sites surrounding their cities. They pass the lines of contractors’ trailers and notice the sign posted on the fence at the entrance to the job site that reads “298 DAYS SINCE LAST LOST-TIME ACCIDENT.” Looking up, they see iron workers walking across beams hundreds of feet above the street. They admire the workers’ courage knowing that at every moment they are in grave danger of falling from the structure to the street below, claiming their lives.

The sight of men and women scurrying around the job site wearing harnesses, hard hats and safety glasses are evidence of the dangers construction workers face every day and the steps they take to protect themselves against the falls, collapsing structures and flying debris that are all understood to be part of the job. Not so apparent, are the silent, unseen atmospheric hazards that exist on nearly every construction job site. The lack of oxygen, the potential for poisonous vapours and the presence of explosive gases present threats to unprotected construction workers and can injure or claim a life as quickly as a slip from an 80-story skyscraper.

Nearly all construction projects entail excavation work at some point during the job. Whether you are excavating the foundation for a new office building or digging the trench in a city street for a new wastewater pipeline, opening the ground can unleash a variety of atmospheric hazards from the earth. The potential for hitting a pocket of natural gas exists during any digging operation. High concentrations of methane accumulated in these pockets will dilute in open air and become explosive quickly. The spark from the tooth of the shovel’s bucket striking a rock can touch off an explosion and fire of catastrophic proportion, potentially engulfing the machine operator and any other workers in the area.

Decaying organic materials that are uncovered or found at the bottom of the hole or trench may be producing poisonous gases such as hydrogen sulphide or carbon dioxide, or robbing the atmosphere of oxygen. In some cases, vapours from other unknown sources may seep into the excavation through fissures in the earth, displacing the breathable air. Workers in the hole may become incapacitated quickly if the oxygen concentrations drop below 16% of volume. It is not always apparent where the danger comes from. Recently a worker was fatally injured while installing a valve in a newly constructed manhole. The oxygen concentration in the pit was found to be less than 5% of volume. The source of the oxygen displacement could not be determined at the time of the accident and remains unknown.

The more traditional acts of construction are not without gas hazards either. Propane gas or diesel powered construction equipment can inject deadly carbon monoxide or NOX vapours into the atmosphere. In cold weather, the use of torpedo heaters on the job site can create carbon monoxide or deplete the oxygen from the air. Explosive gases may leak from compressed gas cylinders used for welding or cutting operations, or workers may be exposed to toxic vapours created from those operations. A worker who is only slightly impaired from a low level exposure to a toxic gas will be more prone to making that deadly slip from the 80th floor.

Finishing operations also present unique dangers to construction workers. For instance, painters wearing supplied air respirators are in danger of being exposed to poisonous fumes in the very air that is intended to provide them with safety. Carbon monoxide from gasoline or diesel compressors, or from the exhaust of nearby vehicles may be compressed into the air supply and fed directly to the worker through the respirator.