Need for Two Air Openings

I write in response to Julius Ballanco’s statement in a column last Fall (Sept. 2006) that there’s no justification for two air openings. Eliminating the requirements for the air openings into a space containing combustion appliances is entertaining an accident with injuries and possibly deaths. All fuels, including solid ones, can break down into gases that include some products lighter than air and some heavier than air.

You’ll recall the requirement isn’t just for two openings, but one low and one high. Given those two, natural ventilation will help ensure this. remove enough of those gases to prevent an explosive accumulation (note that even complying with the size requirements can’t always ensure this).

Another engineer thought he had me on this when he told me that my wood pile wouldn’t break down into explosive gases. He was surprised that I could immediately respond to that one with the story about the farmer who put his wood in an enclosed shed he’d built with no openings in it. To this day, that farmer swears someone must have set his shed on fire. However, I know what happens when you put green wood in an enclosed space. If you don’t, then that helps explain why you can’t understand the requirement for two air openings.
Ken Heselton, P.E., C.E.M.
KEH Energy Engineering
Joppa, MD

Enterprising Pigeons

I have a comment about Mark Bromann’s answer to a question regarding pigeon strips (Nov 2006). I have seen enterprising pigeons place dried vegetation in metal spikes to fill the gaps so they could continue to nest. The vegetation would then create a condition where a fire could flash along the sprinkler line and open more sprinklers than needed. With these strips made of plastic, I can see an additional fuel load from that material. If the strips are kept clean (that is the only way they will work to keep pigeons away), I would agree with your thoughts.
Tom Miller
Varley-Campbell & Associates, Inc.
Oak Brook, IL

Commercial Venting

Julius Ballanco’s Nov. 2006 article on commercial venting was great. I’ve personally been in the plumbing design field since 1966 and have seen a lot of strange designs over those years. I would like readers to understand that a given article is a basic understanding of the subject matter and that there is sometimes much more information to be had by reading codes and manufacturer’s catalogs. Most of the time designers comment that they don’t have a lot of time to do more research.

A perfect example of this is the issue of using Air Admittance Valves. There are some restrictions from using AAVs that many do not realize unless they read the manufacturer’s catalogs. One in particular is that you can’t use these for pumps. Another important point is that even though AAVs can be used in a given building for individual fixtures/groups, there still must be at least one vent extending to open air from the building drain. I believe you touched on that issue when you explained “Rather than connecting to a vent stack...”, but is it obvious to the reader that is what was meant? If a designer wasn’t aware of these items, you can imagine the extras involved on a given project.
Robert E. Liebler,
Sr. Plumbing Engineer

van Zelm, Heywood & Shadford, Inc.
West Hartford, CT