I have no experience, but it looks like Grainger lists some stuff that might give you ideas. It seem there is something called a saddle vent that allows someone to climb up/down a ladder while the vent is in place. And yes it seems they blow air in via a flexible duct all the way to the bottom so the fresh air displaces the bad air. At a manhole I’d think you would be powering an electric fan with a generator, or maybe they have fuel powered ventilators.
https://www.grainger.com/category/safety/confined-space-equipment https://www.grainger.com/product/RAMFAN-Manhole-Entry-System-14H531 Is the manhole dry, or will you also need to pump out water? I also wonder if they require you to have a hoist setup for rescue if a worker gets injured or passes out down in the hole? From: AF <[email protected]> On Behalf Of Chuck McCown Sent: Sunday, February 24, 2019 1:14 PM To: [email protected] Subject: [AFMUG] Manhole ventillation I need to do some fiber work in a metro manhole within the next week or two. In the past, someone else always set up the safety equipment etc. I don’t recall ever being in one that had ventilation running at the time but I almost always see a blower running when others are doing this type of work. This time it will be my oversight and my employees that have little or no experience in manholes. So, I am starting to worry about taking proper care of them. So shopping for guard rails and ventilation blowers today. Found some osha charts on air exchanges etc. If any of you have experience please help me with the following questions: 1) I see duct hoses from 6”-12” in diameter. Seems like you would want a smaller hose so you can get in and out of the cover with the hose in place. a 12” hose would make that difficult I would think. 2) Are most of these blowers 120 VAC? I have found a few that are 12 VDC. Which is preferred? 3) I presume you blow fresh air in rather than suck fumes out? 4) Do you have to have some kind of air quality meter on you when in the hole? 5) Any other safety issues that we need to be concerned with? A manhole safety manual would be a good find. Have not searched for that yet.
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