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A Step-by-Step Guide to Using a Confined Space Ventilation Blower Purge Chart

A confined space ventilation purge chart is an essential tool for ensuring the safety of workers who enter and work in confined spaces. These spaces, such as tanks, manholes, and silos can be dangerous due to the presence of harmful gases and a lack of fresh air. A ventilation purge chart helps to determine the appropriate time in minutes to properly ventilate a confined space. This determination is calculated based on the CFM of air moved by the ventilation blower and the size of the space. In this article, we will provide a step-by-step guide on how to use a confined space ventilation purge chart to ensure the safety of workers in confined spaces.

Understand the Limitations of a Confined Space Ventilation Purge Chart

Before using a confined space ventilation purge chart, it is essential to understand its limitations. The chart is NOT to be used in place of a gas monitor to assess the quality of the air in a confined space. The chart is only to be used to determine the appropriate ventilation rate in time for a confined space to be purged of hazardous air. Even when the chart is accurately followed, the air still has to be tested and retested in order to verify the air in the confined space is not contaminated. Using a purge chart will help reduce the risk of harmful gases and a lack of fresh air. It will not confirm that your confined space has safe air.

Gather the Necessary Information

To use a confined space ventilation purge chart, you will need to gather the necessary information about the confined space. This includes (1) the size of the space, or its volume, in cubic feet and (2) the CFM moved by the ventilation blower. It is extremely important to account for the reduction in CFM that occurs with each 90 degree bend in the blower duct. For every bend, there is a reduction in the CFM pushed by the ventilation blower. This information can be found in the blower specs.

Consult The Ventilation Rate on the Chart

Once you have the necessary information, you can use a ventilation rate purge chart to determine the appropriate ventilation rate for the confined space. To do this, find the size of the confined space on the chart and follow that line to the point where it intersects with the CFM moved by the blower. This intersection point will indicate the appropriate ventilation rate for the space.

Assign Timing Duty

Once you have determined the appropriate ventilation rate, you can begin ventilating the confined space. A competent person will need to verify the blower has run for the time determined by the purge chart. This will ensure that the right amount of fresh air is being supplied to the confined space.

Monitor the Space for Proper Conditions

Once the ventilation has concluded, the confined space is to be tested using an appropriate confined space gas detector. This will confirm the atmosphere in the space is safe for entry. After entry is made, the space is to be continually tested. If, for any reason, the detector alarms the workers are to exit the space immediately.

Follow OSHA regulations and guidelines

Entering confined spaces is dangerous. It is essential that all confined space entry regulations established by OSHA are followed. Proper ventilation, when needed, is only one element of the many that make for safe confined space entry.

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