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The main cause of accidents in confined spaces, according to the Occupational Safety and Health Administration are atmospheric hazards and should preferably be eliminated before entry and kept under control during the stay of workers inside confined spaces.

The concentration of contaminants, the presence of flammables and the inadequate percentage of oxygen, either due to deficiency or enrichment, are atmospheric risks that can cause intoxication and asphyxiation of workers or the formation of a flammable/explosive atmosphere. For Gas Tester Course Get in touch with us

To properly assess atmospheric hazards, it is necessary to know:

The classification of the physiological action of the substance;

The Exposure Limit;

The Value Immediately Dangerous to Life and Health;

The odor threshold;

The density;

The Lower and Upper Explosive Limits;

The flash point;

The auto ignition temperature;

The Safety Data Sheet for Chemical Products:

Various gases may be present in confined spaces. Methane (CH4), formed by the decomposition of organic waste, is a simple flammable and asphyxiating gas. At high concentrations, it displaces oxygen from the air in the confined space. Hydrogen sulfide gas or hydrogen sulfide (H2S), formed in organic matter bio degradation processes, is a toxic gas, chemical asphyxiant and flammable.

Carbon monoxide (CO), formed by burning coal or other carbon-rich materials in the presence of little oxygen (incomplete combustion) and/or high temperature, is a highly toxic and flammable gas. It has great affinity for blood hemoglobin, preventing tissue oxygenation. This can lead to death from chemical asphyxiation. Carbon dioxide (CO2), on the other hand, is a simple asphyxiation and, despite displacing oxygen in high concentrations.

Gases such as H2S and CO can only be measured using dedicated hydrogen sulfide and carbon monoxide sensors. The standard configuration for multi-gas measuring instruments comprises four sensors, one of which is an oxygen sensor, with alarms for deficiency (19.5% in volume) and enrichment (23% in volume); an explosion sensor with an alarm at 10% of LEL; a CO sensor and an H2S sensor.

The H2S and CO alarms can be set to the Tolerance Limit or to the Action Level (half of the Tolerance Limit). The standard configuration contemplates the gases most frequently found in confined spaces, but does not, under any circumstances, dispense with an in-depth study of atmospheric risks to select the appropriate sensors for each case.

Assessment of the atmosphere prior to release:

The recognition of the atmospheric risks present in a confined space is fundamental for the choice of evaluation equipment. The working principle of the sensors (electro chemical, catalytic and infrared) and the effects caused by variations in temperature and air humidity, risks of contamination by other gases and vapors, oxygen volume and measurement ranges must be considered.

The initial assessment of the atmosphere is important to determine the atmospheric risks existing in the confined space, when opening it or to detect leaks that occurred during periods when the confined space remained open without workers inside.

Before entering the confined space, it is necessary to determine the oxygen concentration and the presence of toxic agents inside. The initial assessments must be carried out outside the confined space, through a probe or hose inserted inside it. The use of hoses with a length and diameter different from those recommended by the manufacturer can significantly alter the results of the evaluations. It is not safe to use a rope to lower the equipment and carry out assessments inside a confined space with a vertical opening.

The dimensionless of the ventilation system must consider how the atmospheric risk is created and its concentration, the dimensions of the confined space and the number and size of the openings. The air must be taken from a clean source, free of gases from combustion engines. Long, curved hoses significantly reduce the efficiency of the ventilation system.

Conclusion For Safe Work:

Good confined space safety practices require continuous ventilation, which must be initiated prior to entry and maintained during entry and throughout the activity.