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I am going to be installing an antenna at the top of my brick chimney and I'd like to be able to use a safety line with a fall arrestor. The chimney visually looks OK. I'm trying to figure out the safest way to anchor to the top of the chimney.

So far I've considered two options:

  1. A steel anchor with an expansion bolt into a brick on the chimney. A downside I see to this is that all of the load would be placed on a single brick, and if that one brick came loose, I'd fall. I could improve this by installing two anchor points, but if one brick pulled out I'm not sure I'd have much faith in the second one.

    Steel Bolt

  2. Wrapping webbing around the chimney and anchoring to the webbing. This would be more difficult to install as I'd have to get around the entire chimney, and in the event that the entire chimney was not structurally sound, I risk the entire chimney coming down on top of me in the event I fell.

    Webbing around

Are there any other methods which I might have missed? If not, of these two which would be the safest?

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I'm not an expert, but I don't think I'd trust brick and mortar to hold the weight of me falling. Most brick chimneys can be take out with a few whacks of a rubber mallet, for instance. –  DA01 Aug 7 '13 at 22:15
    
risk can be reduced by planning for a catastrophe (safety harness, ground spotter w/cell phone, ...), and by reducing the likelihood of a catastrophe (top notch staging, low center-of-mass, good weather, no fatigue, sobriety, talking each step through before performing it, ...) –  mike Aug 8 '13 at 0:12
    
I would rent an inflatable bouncy castle! –  DMoore Aug 8 '13 at 17:59
    
That's not the worst idea @DMoore! –  Steven Aug 8 '13 at 19:00
    
I was reading the answers... cringing... boy do I hate heights. –  DMoore Aug 8 '13 at 19:13
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4 Answers

Attaching to the chimney is not a good idea. Just forget about that idea.

If you want to protect against a fall while you are at the top of the chimney, you need to anchor your line at or above your working height. If you don't have anything else near by then you're out of luck.

I recommend looking to to renting a towable manlift.

enter image description here

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There is no reliable data I know of for the ultimate strength of expansion anchors in brick masonry. It's not a viable anchor system no matter how many you use (within reason). You are almost better off with no protection because then you will make damn sure you do not fall. (Just kidding, but there is some logic to this amongst rock climbers).

An anchor system around the entire chimney is a much better option if properly placed. As you note, there is a risk of the entire chimney failing. This risk is difficult to assess, depending on the chimney's age, method of construction (reinforced?), type of brick, the mortar mix used, it's anchorage to adjacent structure, etc. The anchor should be placed as close to the highest chimney anchorage as possible, though it increases your fall distance, it decreases the bending moment in the structure.

If the resulting fall distance is unacceptable, or there is no anchorage, you need to consider alternatives. An anchor system installed into the structure of the building is most secure. This allows possibly a higher anchor (less fall distance) and a more desirable fall factor (proportionally more rope involved for a given fall distance reduces shock loading). This will involve locating structural members and using appropriate fasteners, as well as dealing with sealing around the anchor to prevent roof leaks.

There are manufactured fall arrest anchors suitable to such applications. By following recommended installation instructions, these anchors in the US are OSHA approved and will resist 5000 lbs of force. This is the only sure way of achieving an adequate anchor system.

Incidentally, in the US, OSHA fall protection requirements are not applicable to work done on single family residences.

That's the official line as I know it. That said, I have a similar situation where I sank a single 5/16"x3" solid, shouldered eye screw (hot dipped galvanized) into the center of one roof rafter, straight through the roofing, sealant applied before applying the final few turns. It's been there for decades with no evidence of leakage or corrosion. It does not meet OSHA standards but I consider it marginally adequate in the event of a fall for my particular situation. It will not be adequate for other situations.

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I have found a lot of anchors that can be attached to my roof however my chimney is at least 8-10ft above the highest point of the roof. –  Steven Aug 8 '13 at 1:06
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A suitable ladder stabiliser would provide a little extra extra security.

enter image description here

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I never knew these existed! –  Steven Aug 8 '13 at 19:00
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Why not try something like this:

  1. set up two anchor points, such as large hookeyes, screwed into the wooden siding on either side of the house in line with the chimney
  2. attach a safety line to one hookeye and toss it over the peak if the roof near the chimney
  3. attach to the other hookeye leaving some slack.
  4. attach your safety line to the transverse line.

You could put knots or loops into the transverse line to create natural stops in the event of a slip.

Or you could call in a pro (I hate high ladders and roof work).

.

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I would still fall 8-10' from the top, plus the length of the lanyard (connecting to the horizontal line), plus line stretch. –  Steven Aug 8 '13 at 1:10
    
You could set knots or loops every foot on the transverse line and your harness could be shortened to allow you no more than a foot or two of leeway. You could limit a slip to two or three feet. But consider a stand-in. –  bib Aug 8 '13 at 1:20
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