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Confined Space: Deadly If Not Prepared
“Air monitoring typically is done with a four gas monitor, which monitors for oxygen content, flammable gases (LEL - lower explosive limits) and toxic gases, which typically are hydrogen sulfide and carbon monoxide,” says Lastinger. “These can range in cost from $850 to $2,500, depending on make, model and features.”
Ventilation equipment consists of a fan/blower, duct work and possibly a saddle vent. The major component is the fan or blower, and can be a small unit moving air 800 to 1,500 cubic feet per minute (cfm), to larger units which can move 10,000 or more cfm.
“The size of the space and the tasks to be performed generally determines the volume of air that needs to be moved,” says Lastinger. “Blowers can be electric, gasoline or hydraulically driven. I prefer electric, as there is no chance of the fan inserting carbon monoxide in the space as there is from a gasoline powered fans that I have seen used. Ducting is used to get the air in the space, and to direct it where it is going to allow for the most effective ventilation of the space. A saddle vent goes into a manhole and allows the entrant to enter the manhole without having to remove the ventilation ducting.”
Whenever an authorized entrant enters a permitted space, a retrieval system or methods must be in place, unless such equipment would increase overall risk to the entrant or would not contribute to the retrieving of the worker in the event of emergency.
Lastinger says to enter a permitted space, a worker should use a chest or full body harness, with a retrieval line attached at the center of the entrant's back near shoulder level, above the entrant's head, or at another point which the employer can establish that provides a profile small enough for the successful removal of the worker. Wristlets may be used in lieu of the chest or full body harness if the employer can demonstrate that the use of a chest or full body harness is not feasible, that creates a greater hazard and that the use of wristlets is the safest and most effective alternative.”
The other end of the retrieval line is to be attached to a mechanical device or fixed point outside the permit space in order that rescue can begin immediately, if it becomes necessary. A mechanical device must be available to retrieve personnel from vertical-type permit spaces more than five-feet deep. Generally, this is accomplished using a tripod and a man-rated winch or rope-based retrieval system attached to the worker.