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Two common questions we receive about confined space entry have to do with ventilation. Why do we have to ventilate a confined space? How do we ventilate a confined space properly?
OSHA outlines in 1910.146 Permit Required Confined Spaces why ventilation of a confined space may be necessary. OSHA states, "An employee may not enter the space until the forced air ventilation has eliminated any hazardous atmosphere". So if a gas detector indicates there is an atmospheric hazard, no entry is permitted.
The reasons for this should be obvious. An elevated level of oxygen can be highly explosive. Elevated levels of carbon monoxide or hydrogen sulfide are deadly. And, of course, decreased levels of oxygen are deadly.
When any of these conditions are present, ventilation of the confined space is required. In fact, OSHA states, "The forced air ventilation shall be so directed as to ventilate the immediate areas where an employee is or will be present within the space and shall continue until all employees have left the space".
This is pretty simple really. Drop your ventilation blower duct into the space and turn on the blower. After a period of time, test the space again for any hazards. If the space tests clean, you can enter the space. However, once the space is clean you are not permitted to turn off the ventilation blower. It must remain running during the duration of the entry and the atmosphere must be monitored for hazards.
Good question. There are 8" blowers, 12" blowers, and even 16" blowers. There are confined space blowers that run at 960 cfm all the way up to 2500 cfm. There are gas blowers, electric blowers, and DC powered blowers. Why so many kinds?
The different size blowers provide smaller to larger movement of air volume - more air volume as the size goes up. However, the larger blowers (12" and 16") take up considerably more of your manhole opening. This can prove to be inconvenient.
The different power supplies are simply for convenience. The most common is the electric blower which is typically run off of a generator. The blower to the left is the Ramfan UB20 blower equipped to run off of 12 VDC.
The different cfm (cubic feet per minute) options simply translate in to faster atmospheric refresh or turnover times. All of them will do the job. But the higher cfm blowers will do the job faster. Manhole vaults and similar spaces usually don't require massive amounts of cfm to ventilate properly.
The blower on the left is our most popular blower - the Allegro 9533-15 ventilation blower. It is suitable more most applications. It is included with most of our Confined Space Contractor Kits. It is also our most popular blower.
For more information on the time it takes to ventilate a space, please download this pdf - Confined Space Ventilation Blower Purge Chart.