Extraction Fan Causing Building Roof Implosion?

Yes, this is plausible. I haven't personally encountered any instances, but I know of blast freezers that have squished from cooling, and controlled atmosphere rooms that had plywood pulled off from interior walls when certain valves failed.

a properly sized and installed barometric damper would prevent the scenario

Never heard of such a thing.....did hear of a 20k cfm exhaust fan collapsing a garage door once, but no confirmation....

No.

One Pa equals 1.450377×10⁻⁴ psi, therefore 1,000 Pa equals 1.450377 x 10-¹ or 0.1450377 psi. Much more pressure than this can be achieved by blowing through a straw in a soda glass or beer glass if you choose. The fans you are referring to are high volume low pressure units. They have large clearance around the fan blade and high pitched blades. Their rotational speed is comparatively slow to other fans. The fans shown in #3 are of this type. They are used in barns, hen houses and such in order to cool the animals with a high volume of air but low pressures to prevent animal health problems. They are also used in large commercial flower nurseries to keep flowers and such cooler during hot summer months. Closing all the vents and doors of a cheaper "hoop" style green house with a polyethylene sheet used as the walls and ceiling while the fan is exhausting air won't even cause your ears to "pop". If the plants are watered prior to using the fan, evaporation cooling makes them even more effective.

The large fans on the top of buildings are high volume low pressure fans. This prevents the damage you were referring to but moves great amounts of air. The Positive Pressure Fans used by firefighters to exhaust smoke or flames from a building are also of this type. The fans used to blow up hot air balloons prior to applying the propane heat also are this type. In that case anything other than a low pressure high volume fan would damage the nylon balloon.

Good Luck, Old Salt

Lets carry those numbers a little further. 0.145 psi x 144 ≈ 21 pounds per square foot. That is a substantial load for a roof structure (don't have access to my code books at the moment).

Yes, it is possible to cause the collapse or "implosion" of a roof, particularly if the structural strength of the steel had been compromised by a fire's heat or if the design was marginal at best.

--John M.

Nothing was said about a fire compromised roof in the original posting. Also nothing was said about a marginal design. All criterias were based on a structure that met minimal code requirements. The original question asked if this particular type of fan would collapse buildings. No it won't since the fans do not create enough negative pressure (vacuum) to do so. The fans move a high volume of air at extremely low pressures.

21 pounds per square foot is not a substantial load when the normal/average/regional average minimum load requirement is 30 lbs/sq ft. where snow is a potential problem. If proper and at least minimum drain sizes are installed rain should not be a problem except is extreme torrential downpours.

The types of fans described by the OP do not have the capability to reach pressures that would create enough vacuum to imploded a building which met codes and continued to meet codes during its life. The places they are used require large amounts of air to be moved. For a fan with a fixed horse power motor the more pressure the less volume. That would be extremely wasteful since volume is wanted and not pressure. The applications are high volume units with the least possible pressure. With water an internal pressure of a building at 21 lbs/sq ft (0.145 psi) the equivalent pressure is 4 inches of H2O, indeed a very low pressure.

Based on my personal experiences consulting for a large greenhouse company (25 acres under glass and poly) there is little to no chance of a roof collapsing if it meets code. The identical fans in the OP are used there in the greenhouses. The same is true of the fans used by fire fighters for positive pressure ventilation. I have never collapsed a residential, commercial, industrial or agricultural roof with this pulling air out of a structure. The same units are used to inflate hot air balloons prior to heat application, high volume low pressure.

The extremely low occurrences of fans collapsing buildings is also indicative. A building or roof can not be collapsed it the fans being used are not capable of the obtaining the pressures needed to do so.

Good Luck, Old Salt

The OP stipulated that the fans could produce 1000 Pa and more, and also that the roof trusses were already undersized.

Again, the fans used to evacuate air/gasses from a building are not designed nor capable of obtaining those pressures of 1,000 Pa or more. How can something be done if the system is incapable of doing it? The OP can stipulate what ever he wants but if the units he is stipulating are incapable of attaining those conditions how can it work?

If the roof trusses were already undersized were they undersized enough to be a problem with the lower pressure capabilities of the fans? The trusses would have to be extremely undersized to accomplish an implosion.

Just like spheres, buildings are much easier to explode than to implode. There are many explosion panels on buildings but seldom are there implosion panels since it so seldom happens.

Good Luck, Old Salt

You are wrong about spheres, too.

Whatever. Ever try to explode or implode a tennis ball? An explosion enclosed within a sphere will product much higher pressures than the explosion outside the sphere. The internal explosion has no place to dissipate the forces while the external has all but a small part in contact with the sphere to dissipate the forces. Same effect as a balloon.

Good Luck, Old salt

You're wrong about that, too.

Hopefully you don't think I am wrong about these questions:

How many submitters to the OP are guessing with their replies? How many are hypothesizing about the fans and building construction? How many are familiar with building construction? How many are acutely knowledgeable about roof and wall loads in the various types of building construction? How many have even seen a picture of this type of system? How many have seen, first hand, the various types of fans used to purge buildings with fresh air. How many know if positive pressure or negative pressure is better and can accomplish the job quicker? How many have seen this type of system? How many understand the system? How many understand what the user is trying to accomplish after seeing one in operation? How many understand the operation and construction of this type of fan? How many have operated and trouble shot this type of installation? How many have designed and engineered these systems? How many really know what they are talking about? How many have operated a portable unit used for the same purpose? How many are fire fighters, hot air balloonists, greenhouse personnel or horticulturists who understand and have had hands-on experience operating the portable version of these fans? How many are building operators and have operated, understand and have trouble shooting experience on their systems?

Having reviewed this forum for seven years, most of the submitted answers to everything are probably on the light side including this blog. Am I also wrong about that, too?

Good Luck, Old Salt

Well said Sir.

You are not necessarily wrong about the many light (or lightheaded) replies. But your tone is wrong, and you are talking to the wrong person. I have had experience with buildings "imploding" and am familiar with concepts of building and pressure vessel design. Vessels withstand internal pressure better than external, and so do tennis balls. Hell, you can squeeze a tennis ball.

I don't know how you could conclude that tone of my questions about the skills of the contributors. They are all valid questions and not presented in an argumentative manner. Simply asking about the skills of some who claim to be experts but in reality have only basic or no legitimate knowledge of the subject (not including light hearted answers). If my questions were not clear to the readers, I apologies to them for what seemed to be clear to me but apparently not clear to all who read it. Except for the apparent misconstrued tone of the submission, those questions have most likely been thought of by everyone on CR4. In my readings of this forum there are certainly many others that have expressed the same questions as I did.

Your experiences are to be commended. Your skills seem to fit in with a good and intelligent answer to this question. I too have experience in some of the facets of the original question. They include many types of fans including the application of those directly mentioned. This knowledge was obtained through designing structures with thin roofs and wall that were cooled with ambient air and those fans. It also was obtained through inspections and discussions with those who operate buildings with those exhaust fans to remove potentially extremely hazardous substances vapors (applicable permits obtained for these operations). Along with that was the design, fabrication and installation of reactors from 5 gallon to 5,000 gal with steam heating and water cooling. That's why dimpled shells are my preference instead of stay bolts. Same for boilers up to 1,000 hp and 250 psi. In other words we both apparently know what we are talking about. You from one view point, me from another.

Hopefully the tone of this will not be mistaken. Although as with teaching and learning, the quality of the teaching is not the methods or standards, it is how well the students retain and utilize the knowledge given them. Same with CR4 from my viewpoint and apparently others.

Also I have investigated one building that imploded but under much more severe conditions. Still have the same viewpoint about the OP.

Good Luck, Old Salt

Lets say the roof support was undersized and the rood would have collapsed anyway at the slightest load like wind, rain snow the chimney sweeper ...

All you can do is to add another 14.7 psi of pressure onto the roof load by evacuating the place.

If the roof can not support that ...

... well again, it would have collapsed anyway. The fan will just be a bloddy excuse!

Oh and btw in case a fire was in the building it could damage the structural support. What are you going to blame then???

You mentioned "fire" - but indeed there had been fire during construction works (some 2010 or 2011) in one place of the roof of the unlucky supermarket that collapsed at the end of the 2013 !

Investigaters have made an experiment with controlled fire on the remnants of the roof this summer beginning to proof whether constructions might have been damaged and what might be the major cause.

However, I don't know what they found.

You mentioned fire first!

What are you actually trying to prove?

I installed one of these systems in the atrium of the International Conference Centre in Birmingham, UK. The purpose is the remove smoke so that people can evacuate the building, and then the vents/fans are shut off to starve the fire of air. The fans are interlocked so they will not start until the inlet vents (in this building windows at first floor level) are open. It is fitted with two independent systems each having their own pre-stored air supply and fed the window actuators through copper pipes so a fire or power failure/shut off will not disrupt the operation. Shutting down the fans once the building is evacuated can only be manually selected by the fire crews.

You better tell these guys!

http://en.wikipedia.org/wiki/Berlin_Brandenburg_Airport

"... On 8 May 2012, it became clear that the building could not open on schedule due to failure of the fire protection system. All trials were halted and have not resumed. ..."

Thank you for the link, I was unaware of this but will follow it closely in the future. Having worked with German companies for many years I have long known that the myth of German efficiency and engineering competence is more about marketing and PR than reality.

This appears to be another example of architects valuing aesthetics over practicality and failing to understand basic engineering. Add oversight by politicians who know nothing about control systems and chaos follows. Airports by definition are functional buildings that annually deal with millions of passengers. Smoke extraction ducts are part of that functionality. In the ICC in Birmingham, the smoke extraction fans are set into the glass roof for all to see. They vent direct to the outside without any ducting, and as a result are aesthetically pleasing. (To me at least. Prince Charles called it a "carbuncle", but he is not an engineer and does not comprehend that function must take priority over form) If the architect does not want to show ducts on the roof, incorporate into the design an additional a false roof over the ducts. That has to be more cost effective than placing the ducts under the floor. Attempting to defy the laws of physics by getting smoke to move downwards in a fire is more than incompetence, it is crass stupidity. Not fitting smoke detectors and sprinklers under the roof because they don't look pretty, breaks most fire codes and whoever approved that feature should be pilloried. Electrical wiring is statistically one of the prime places where fires start. Relying on actuators that operate electrically without a fail-safe local mechanical/pneumatic/hydraulic backup with built in power storage is criminal.

The major failure is not the construction errors and delays, it is that this design ever got beyond the drawing board.

The tragedy happened in Riga, in the so called Maxima Zolitude supermarket 21 November last year - you may "google" and found yourseves about it

I don't know what the findings will be, but THIS thought expressed here - I believe - is ONLY mine

I was down there inside the building some 100 minute before the collapse

At that moment an alarm turned on and administration - rather weakly - was asking people to leave the building. Nobody left however before they finished shopping as nobody took the alarm seriously. I believe there began first disruptions in the construction and some signalization sensors had felt it and produced the alarm

What makes me believe a fan may be "the last straw" is that because the mentioned 100 minutes before the tragedy when I was going on to the exit I felt at one and the same time a wave of fresh breeze and the tobacco smoke. There always stayed smoking people before the entrance but I never felt the smoke inside before. That made me believe later a powerful fan turned on. Later on, also, I read that just moments before the collapse the entance doors jammed in closed position.

Anybody ever tried to open an exterior door with the air make ups running to the negative in a large manufacturing facility in the winter? my guys closed the intakes cause they were getting cold due to the volume of outside air being brought in (it was about 0°f), can't say as I could blame them as it was rather chilly in the plant but I wish they had throttled back the fans instead.

Back to the original question, Don't think you can get but 14.7 psi (atmospheric pressure) no matter how high the vacuum is but that still makes opening an exterior door a massive undertaking. Try it sometime 7' x 3' door running about 4"h2o you gotta put some butt behind it, had some of the smaller ladies in the plant asking big guys to open the door for them LOL, kinda funny but I still caught hell for it.