What it is and why it is dangerous
Carbon monoxide, identified as CO, is a toxic gas that can be produced by the incomplete combustion of carbon-containing materials. It should not be confused with carbon dioxide, CO2: they are distinct agents with different hazards and detection systems. An assessment that only considers one does not automatically rule out exposure to the other.
Carbon monoxide (CO) does not offer a reliable warning through smell or color. A person can be exposed without recognizing it and lose the ability to react before leaving the area. Prevention should focus on the sources and conditions of accumulation, avoiding relying on the senses of those working as a warning system.
Job sources that need to be identified
Potential sources include combustion engines, generators, power tools, vehicles, heating equipment, and thermal processes. The assessment should include owned, rented, and contractor-operated equipment. A machine temporarily brought in for maintenance can create a scenario that was not present during normal operation.
The location of gas discharges is also studied. An external source can affect the interior if its emissions reach an air intake, door, or opening. Location, operation, and surrounding environment are all important factors, not just whether the equipment is outdoors. Occupied areas near the main work area must also be considered.
Situations that favor exposure
Indoor spaces, partially enclosed areas, and rooms with insufficient ventilation can promote accumulation. Opening a door or noticing air movement alone does not prove that the concentration is safe. The geometry, the amount emitted, and changes in conditions all influence the outcome.
Confined spaces require a specific assessment and procedure that covers all their hazards. However, the risk of CO exposure is not limited to confined spaces: it can occur in a warehouse, construction site, or ordinary work area. The expected duration of exposure does not justify ignoring it, because a dangerous concentration can develop rapidly.
Prevention at the source
The first step is to avoid introducing a CO source in a location where it could expose people. When feasible, electric, battery-powered, or other technically suitable alternatives are studied, also assessing their risks. NIOSH advises against using gasoline-powered equipment in buildings or partially enclosed areas due to the risk of carbon monoxide accumulation.
Combustion equipment and its exhaust systems must be maintained and operated safely. Ventilation and extraction require proper design and testing, not an assumption based on room size. Temporary work plans must identify who authorizes the equipment, where it is located, and how protection is maintained throughout the task.
Measurement, detection and alarms
The assessment determines when continuous measurement or detection is needed and what equipment is suitable for CO. Range, location, maintenance, functional checks, and alarm response must be considered. A detector for another gas should not be assumed to be capable of measuring CO if that function is not specified and verified.
Action levels are established by competent personnel, taking into account the purpose of the system, the assessment, and applicable standards. Occupational exposure levels should not be used as alarm settings without analysis. The presence of a detector does not authorize unsafe work practices, nor does it replace emissions control.
Warning signs and response
Exposure may be accompanied by headache, dizziness, nausea, confusion, or loss of consciousness, among other effects. These are nonspecific signs and do not, on their own, confirm the cause. If exposure is suspected or an alarm is triggered, the area is evacuated to uncontaminated air, and the established emergency response is activated.
Urgent assistance is requested by calling the local emergency number, 112 in Spain. Do not re-enter the area or attempt an improvised rescue that could endanger others. Intervention in a hazardous atmosphere requires trained personnel and appropriate equipment. Resuming work requires eliminating the cause and verifying the conditions according to the established procedures.
Practical example
A contractor proposes using a combustion engine cleaner inside a work area. Before starting, the coordination team discovers that emissions were not accounted for in the plan. Alternatives are reviewed, and a system is selected that avoids bringing the engine inside, with an evaluated exterior location away from potentially affected air intakes.
The planning process also identifies nearby occupied areas, communication between teams, and suspension criteria. Actual execution is verified, not just prior documentation. If the location or equipment changes, the authorization is reviewed: safety depends on the entire scenario, not on having performed similar work previously without incident.
Common mistakes and follow-up
The most dangerous mistakes are relying on smell, considering an open door sufficient, or thinking that a small motor cannot generate significant exposure. Another dangerous mistake is confusing a household or other contaminant detector with a system validated for the required workplace purpose.
Monitoring reviews source inventory, maintenance, temporary work, and practical alarm training. Every incident or equipment change must be added to the assessment. Information on CO (carbon monoxide) must also reach purchasing, leasing, and contractors to prevent a new source from appearing on the job without its consequences being anticipated.
