Sorry, No Pics, But...

[Glennman CBO]

Had a funny but scarry one the other day.

I suppose this could fit under fire, or mechanical, but it involves trusses, so I put it here.

Inspected a paint booth. There are (2) approx 24" exhaust vents going into the attic, and extending out the roof. I looked in the attic from the access point and it appeared that the wood trusses had been cut to accomodate the vents. The attic at this area (near the ridge) is approx 8 ft high, so there would be the bottom chord, at least one web, and the top chord involved at each vent. The roof slope is approx 6/12.

I wrote the correction to provide engineering for the truss repair that would be required (among others).

The gentleman procceded to explain to me that the trusses have not been cut, but rather that trusses were fully intact. He continued to expalin that he wrapped the truss members with sheet metal, and that the truss members were INSIDE the vents. He said that he contacted the truss company, and this was the advice they gave him. He actually enclosed the vents around the trusses!

I asked him for the correction notice back so that I could make the changes to the correction. He appeared relieved when I completely scratched the correction, but his demeaner changed when I reworded a new one at the bottom (as you can imagine).

Yes, they are out there.

 

Re: Sorry, No Pics, But...

Glennman CBO,

This one got me to thinking. When that happens I start with what are the reasons to say no. In this case about the only thing I can think of is, if the building is sprinkled the trusses now have no coverage for that portion that is inside the vent. That can be fixed. The spray booth has fire suppression and it may be possible to provide protection inside the vent. It may even exist already. If it does exist it may need alteration as it is not meant to provide the same type of protection as a building sprinkler system. The other choice would be to drop a couple heads.

The vent is exhausting clean ambient air. I don't see a problem with that. The truss may disrupt the air flow but here again, I doubt it will be a problem. There is a listing for the spray booth but single wall vent has no listing and I doubt that the spray booth's listing included the vent.

So help me out here and tell what I am missing. I didn't think about it all that long so don't worry about embarrassing me.

 

[Glennman CBO]

Re: Sorry, No Pics, But...

Tiger Loose,

In the jurisdiction I used to work for, we were greatly encouraged to think outside the box. Once I found a ground wire that was passing through a plumbing vent in a wall. It happened during a previous remodel, and was now exposed during a flood repair. I took pictures and showed it to all my peers, including the BO. After laughing and carrying on about it, the BO said "where does the code say you cannot have the wire passing through the vent?" Well, from a plumbing stand point, I suppose one could seal the hole to make it gas tight, then there would be no violation, I guess. The point was to not jump to conclusions and assume that everything we find that is wierd must be a violation.

I tried that approach. But, in this case I believe there are several violations.

The vent is carying more than just clean ambient air. Per 2006 IFC section 1501.1 and 1502 the paint booth is conveying exhaust from a flammable finish application process, and 1504.3 dictates design and construction of paint booths. 1504.3.2.5 gives minimum clearance to combustible walls, ceilings, and roofs, and more specifically exception #2 states that if the booth is closer than 36" from a wall or roof assembly, then the wall or roof must be non combustible (or 1 hr interior wall, and non combustible exterior wall, exc.1).

Now, this is referring to the booth itself, and not the vent. The vent (per IFC 1504.7) is regulated by section 510 of the IMC. This section regulates "hazardous exaust systems". Section 510.8.2 deals with clearances to combustibles, and table 510.8.2 states that ducts that convey flammable vapors require 6" clearances to combustibles. This of course is refering to clearances to the outside of the vent, because I think the code assumes that the combustibles would be on the outside of the vent, not on the inside.

I don't believe that wrapping the truss with sheet metal is an approved assembly.

The automatic fire extinguishing system that is required for the paint booth and its exhaust duct by IFC 1504.4 does not reduce or eliminate the clearances to combustibles requirements of the vent or the booth, since both are required.

Another issue they have that I didn't mention in the original post is that the top of the booth is about 2" from the combustible ceiling. The ceiling has no rating, and IFC 1504.3.2.5 states that not only do they need a 1 hr rating, but the area on the top mst be accessible for cleaning. I suppose they can figure out a way to clean it, but there is still the 1 hr issue.

 

Re: Sorry, No Pics, But...

Glennman CBO,

Since I do not deal with the IFC, I am not all that familiar with the FC. I was not aware that the fire code treats a product conveying system for a paint booth the same as a grease hood exhaust system. Additionally, I have not found the references you quoted and we are looking at different code books. Mine is based on the 2006 UMC.

As to what is being conveyed; The Ca, Air Quality Management District {another regulating body} requires that the exhaust be filtered to the point of nearly clean air, if there is such a thing in Ca.

 

[Glennman CBO]

Re: Sorry, No Pics, But...

As to what is being conveyed; The Ca, Air Quality Management District {another regulating body} requires that the exhaust be filtered to the point of nearly clean air, if there is such a thing in Ca.

I guess in California, the filters and fans would have to be reversed. :lol:

I don't know how clean the filters make the exhausted air. One can see right through them. Years ago (in my chimney sweep business, late 80's), I used to clean the paint booth flues for a RV outfit on a quarterly basis. I came out the same color as the RV's. I don't know what kind of filters are required, but the ones in this man's booth don't look much different that the ones I used to see.

 

[AegisFPE]

Re: Sorry, No Pics, But...

Table 510.8.2 states that ducts that convey flammable vapors require 6" clearances to combustibles. This of course is referring to clearances to the outside of the vent.

This sounds like a good comment for the described condition. It sounds like the installer was trying to keep the joists out of the vent, but failed to maintain the 6-inch clearance.

Perhaps if there was sufficient free area within the vent, the installation could provide 6-inches clearance around each truss. Then you could look parallel to each truss and view that it didn't penetrate into the vent, but that the vent wrapped around it. However, such an arrangement may be more prone to accumulation of conveyed material.

 

[RLM-Architect]

Re: Sorry, No Pics, But...

Other Standard that would apply here is and NFPA 33.

"G" is right, the exhaust air is anything but clean.

The air is also combustible from a pint booth.

The duct should have been relocated or made to circumvent the truss.

Good call.