Controlling Toxic Atmospheres
One primary control measure effective in preventing toxic hazardous atmospheres from developing in the first place is the use of less toxic products that vaporize less readily.
Selecting the Right Blower
Keep less of the product at the site and keep containers closed inside the confined space at all times.
Ventilating Confined Spaces
Ventilation is one of the most common control methods used in confined spaces to eliminate hazardous atmospheres.
Ventilation helps to:
- provide adequate oxygen to the air in the space
- control atmospheric contaminants
- prevent fire and explosion hazards
- control heat and humidity
When ventilation is used to remove atmospheric contaminants from the confined space, the space should be ventilated until the atmosphere is within the acceptable ranges. Ventilation should be maintained during the occupancy if there is a potential for the atmospheric conditions to move out of the acceptable range.
Once it has been determined that the confined space contains a harmful atmosphere, the next step is to clear it. Ventilation blows out oxygen-deficient or contaminated atmospheres and replaces harmful vapors with clean, fresh air. Make sure to ventilate the space thoroughly so that there are no contaminated pockets left, and then test the atmosphere again.
For permit spaces that are deep or have areas leading away from the entry point, the atmosphere may be layered or may be different in remote areas. For these spaces, testing must be done in the area surrounding the worker, which is considered four (4) feet in the direction of travel and to each side. If a sample probe is used to do the testing, then the worker must move slowly enough so that testing is completed, keeping the equipment "response time" in mind, before he/she moves into the new area.
Welding, cutting, burning, and continuous brazing generate hazardous fumes and dusts that can be more effectively removed by local exhaust ventilation systems at or near the point of generation.
When ventilation is not possible or feasible, alternate protective measures or methods to remove air contaminants and protect occupants should be determined by the qualified person prior to authorizing entry.
Continuous Forced Air Conditions
Conditions regarding continuous forced air ventilation should be used as follows:
- Employees should not enter the space until the forced air ventilation has eliminated any hazardous atmosphere,
- Forced air ventilation should be so directed as to ventilate the immediate areas where an employee is or will be present within the space,
- Continuous ventilation is maintained until all employees have left the space, and
- Air supply for forced air ventilation should be from a clean source.
Knowledge Check Choose the best answer for the question.
6-3. When testing for hazardous atmospheres in a confined space, the area surrounding the worker is considered _____.
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