Distribution Centers – Part 1: Smoke Venting and the Art of Confusion
By Jeff Harrington, CEO and Founder of Harrington Group, Inc.
One thing most distribution centers have in common is storage of goods to heights exceeding 12 feet. A fire in such a facility can generate significant amounts of smoke and heat and it is a good idea to get rid of them, right? Such a simple question should have a simple answer, right? Well, if that were true, then this article would be almost over, right? Wrong!
Let’s first look at NFPA for some guidance. NFPA has a document devoted to the issue of smoke and heat venting entitled “Guide for Smoke and Heat Venting” (NFPA 204M – 1991 Edition). This document provides 22 pages of design guidance on how to automatically remove smoke and heat from unsprinklered single-story buildings.
Section 6-1 emphasizes that the vent design criteria within NFPA 204M is relevant in the absence of sprinklers and that no broadly accepted equivalent criteria exists where sprinklers are present.
So, what do you do if you have a sprinklered warehouse building? Well, NFPA has numerous standards covering the design of sprinklers for various warehouse occupancies.
NFPA 231C deals with rack storage in warehouses. Section 3.3 says the sprinkler design criteria contained within are valid only in the absence of roof vents and draft curtains.
NFPA 231D addresses tire storage and discourages the use of smoke ventilation until after control of the fire is achieved. NFPA 231F deals with rolled paper storage and takes the same approach.
Several conclusions can be drawn from a review of these NFPA documents. Automatic smoke and heat venting in an unsprinklered warehouse is a good idea and there are concise design methods to do it effectively. Automatic smoke and heat venting in a sprinklered warehouse may not be a good idea. No design methods are currently available to achieve effective smoke removal performance in a sprinklered building. No sprinkler system design criteria are currently available which specifically account for the effects of an operating smoke and heat ventilation system.
It seems to follow, therefore, that providing automatic smoke and heat venting in a sprinklered warehouse does not represent sound engineering judgment.
What do the model building codes have to say on this subject? Let’s look at the three predominant ones: SBCCI (Standard); ICBO (Uniform); and BOCA (National). All three have specific provisions that require automatic smoke and heat ventilation in warehouses.
Each has certain conditions and exceptions, the complexity of which is too much for this article.
Very simply, each of these model codes has requirements that mandate the provision of automatic smoke and heat ventilation in both sprinklered and unsprinklered buildings. The design criteria for this ventilation are the same for both sprinklered and unsprinklered warehouse buildings and are taken from NFPA 204M guidelines that relate to only unsprinklered buildings.
This is a good time to stop and pose some questions designed to get you thinking, and hopefully even stir up some controversy.
- How can the model building codes mandate automatic smoke and heat ventilation systems in sprinklered warehouses when…
- no sprinkler design criteria is available which accommodates for the possible detrimental effects of the ventilation on extinguishing effectiveness and…
- No ventilation design criteria is available which accommodates for the various effects of the sprinkler system on the fire, fire plume and smoke layer characteristics?
- Why do the model building codes require the use of the same smoke and heat ventilation design criteria based upon NFPA 204M for both unsprinklered and sprinklered warehouses when NFPA 204M clearly states that the criteria is valid only for unsprinklered buildings?
- For example, why should the building owner have to install costly curtain boards in a sprinklered building equipped with mechanical ventilation fans when their function is to make gravity-type vents work effectively in unsprinklered buildings?
What do you think? I’d like to hear from you. Contact us with your comments or opinions.