Fire & Life Safety: Laser-Tag Operators Burned by RTU Duct Detectors

Q. Our customer operates a large indoor electronic paintball arena. Instead of one hit from a stinging paintball, the special vest worn keeps track of, among other things, how many times players are ‘hit’ and who ‘shot’ them with the laser gun. Hits are registered when the vest flashes. Customers let loose in a converted big-box store with platforms and plywood buildings and other objects setting the course. The lights are dimmed and the fun begins—the thrill of the hunt is made all the more exciting by fog machines. The problem is that the local fire department is dispatched at least three times a week because of the activation of one or more of the roof-top unit (RTU) duct smoke detectors. What’s the solution?

A. These same theatrical fog machines are used in other businesses and operations such as nightclubs and stage performances. Having played laser tag before, I knew a little about the game, but I know more about the use and mis-use of duct smoke detectors. The first thing you have to know about duct detectors is they are not considered a requirement for the installation of a manual, automatic or combined automatic-manual fire alarm system. In fact, the requirement for their installation is found in the International Mechanical Code, part of the HVAC contractor’s responsibilities. The rules for when they are to be installed and when they should not be are spelled out. In the case of RTUs, the wording is clear. “Exception: Smoke detectors shall not be required where air distribution systems are incapable of spreading smoke beyond the enclosing walls, floors and ceilings of the room or space in which the smoke is generated.”

This exception goes back to the heart of the proper use of duct detectors, in that duct detectors are required so that smoke and gases from the fire area are not spread to other parts of the building, which could cause panic and threaten lives.

When duct detectors are used in many RTUs, it is because the person “requiring” their installation plans on using them as early detection of fires. Duct detectors are not good in providing early detection duties. In addition, if a fire alarm system is not required for a building the duct detectors would be relegated (by the Mechanical Code) to merely cause an LED and sounder to activate a test-reset station; not cause a building-wide evacuation. The alarm contractor interacts with the duct detectors when a building is required by the building/fire code to have a fire alarm system installed and the duct detectors are also required to be installed by the Mechanical Code. If they are both required, then it is mandated by the building/fire code to indicate their activation (a lot better than the mechanical contractor would do with their single remote test/reset station) and signal at the FACP, annunciators and at the remote central station.


Know where to find requirements

Don’t overlook the significance of the fact that voluntarily-installed fire alarm systems do not have to tie in any duct detectors. The 2009 building/fire code introductory paragraph on duct detectors stated: “Smoke detectors installed in ducts shall be listed for the air velocity, temperature and humidity present in the duct. Duct smoke detectors shall be connected to the building’s fire alarm control unit when a fire alarm system is required by Section 907.2. Activation of a duct smoke detector shall initiate a visible and audible supervisory signal at a constantly attended location and shall perform the intended fire safety function in accordance with this code and the International Mechanical Code. Duct smoke detectors shall not be used as a substitute for required open-area detection.”

Go to bat for your customer and educate inspectors and engineers on the proper application of these important devices. Your supporting documentation is already there, now that you know where to look. Simply because RTUs may come from the factory with a duct detector built-in doesn’t mean you have to cause a building wide evacuation, or even hook them up!


Greg Kessinger is SD&I’s longtime resident fire alarm and codes expert and a regular contributor. Reach him at