Disclaimer: This resource has been prepared to help the workplace parties understand some of their obligations under the Occupational Health and Safety Act (OHSA) and regulations. It is not legal advice. It is not intended to replace the OHSA or the regulations. For further information please see full disclaimer.
(Refer to the flow charts on Atmospheric Hazards at the end of this Section)
The plan must contain provisions for atmospheric testing. The testing must be done as often as necessary before and while a worker is in a confined space. The atmospheric hazards of concern include oxygen content outside the acceptable range of 19.5 to 23%, the potential accumulation of flammable, combustible, or explosive agents, or accumulation of atmospheric contaminants.
The employer must appoint a person with adequate knowledge, training and experience to perform adequate tests. The testing is required as often as necessary before and while a worker is in a confined space to ensure that acceptable atmospheric levels are maintained in the confined space in accordance with the relevant plan.
Representative sampling should take into consideration the presence of stratified atmospheres and pockets of contaminated air within the confined space. The selection of testing equipment will depend on the circumstances of the confined space, the nature of the work within the space, and knowledge of possible atmospheric hazards. Whenever practical, continuous monitoring should be considered. Equipment performance characteristics to be considered include, but are not limited to: principle of detection of the hazards of concern, specificity, interferences, detection concentration range, response time, calibration requirements, and intrinsically safe equipment for spaces with potential accumulation of flammable hazards.
All workers involved with confined space entry should be trained to understand the testing results, in accordance with the relevant plan.
Instruments used for measuring atmospheric hazards should be calibrated as per manufacturers' requirements. The testing instrument must be selected and calibrated for the specific atmospheric hazards likely to be present in the space as identified in the relevant assessment. Equipment maintenance and calibration records should be kept.
Yes, but for general survey instruments with sensors that respond to many different chemicals with similar properties, the person performing the tests and the users of test results need to understand the specificity and relative response characteristics of the instrument for proper interpretation of results. For example, a combustible gas instrument that uses pentane as the calibration gas will measure other combustible gases such as methane with a different response characteristic. In this case, the actual concentration of methane will be determined by applying a correction factor to the readout of the instrument.
When the exposure is to an unknown mixture of atmospheric contaminants or combustible gases, the testing results need to be interpreted by a person with adequate knowledge, training and experience about the confined space hazards of concern and the testing equipment.
Continuous monitoring is required:
Even though a continuous monitor may have data logging capability, results must still be recorded at adequate intervals as determined by the plan, above and beyond the data logging printout or electronic storage. This ensures that workers are actually aware of the levels they are encountering and aware of any fluctuation that may be occurring in order to warn them of any unusual conditions as they develop. Monitors may have alarms; however, depending at what level they are set, they may not give the workers adequate warning of fluctuations or increases in atmospheric levels that should be investigated.
The frequency of recording test results is determined by the confined space plan, based on the potential for accumulation and possible fluctuations of the atmospheric hazards as determined by the assessment.
In general, the employer must retain atmospheric testing records for the longer of the following periods: one year after the document is created; or, the period that is necessary to ensure that at least the two most recent records of each kind that relate to a particular confined space are retained. For confined spaces with multi-employer involvement, the constructor or employer (as the case may be) responsible for creating the record shall retain the record. On construction projects, the records must be kept by the constructor or employer (as the case may be) for at least one year after the project is finished.
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