In our line of work we come across a lot of mechanical ventilation systems that are intended to control/reduce quantities of hazardous gases/fumes/vapors in processing/work/storage areas. And in many cases the facility will hand us a document from a designer/contractor that shows the ventilation system has fans that can meet the CFM prescribed in their chosen RAGAGEP or applicable OSHA standard; however, when we examine this “ventilation design basis” there is no documentation of how the ventilation system actually works: 1) where is the make-up air coming from? and 2) where is the bad are being discharged? These two (2) components are HUGE in ensuring a ventilation system is doing what we hoped AND is not creating a hazard elsewhere or worse, providing a FALSE sense of hazard control. We like to refer our clients to their state Mechanical Code (if their state has one) or even to the International Mechanical Code (IMC) as a baseline for their ventilation design, as many of the RAGAGEPs focus on the air flow calculations and not some of these very basic design features. For example, it is not all that uncommon to find the ventilation intake(s) and discharge(s) on the same wall or ceiling, even though the facility can provide us with fan spec’s and intake size to show that the air movement meets RAGAGEP numbers (see my previous article on the locations of intakes). The way the air moves through the space can be just as important than how much air is moved! Case in point, check out these BASELINE ventilation requirements from the 2015 IMC…
NOTE: many state mechanical codes will contain this same language, so if your state has been adopting the IMC for the past decade or so, there is a good likelihood that your state mechanical code will contain these requirements.
(emphasis added by me)
502.8 Hazardous materials – general requirements
Exhaust ventilation systems for structures containing hazardous materials shall be provided as required in Sections 502.8.1 through 502.8.5.
502.8.1 Storage in excess of the maximum allowable quantities
Indoor storage areas and storage buildings for HAZARDOUS MATERIALS in amounts exceeding the maximum allowable quantity per control area shall be provided with mechanical exhaust ventilation or natural ventilation where natural ventilation can be shown to be acceptable for the materials as stored.
Exceptions:
- Storage areas for flammable solids complying with Section 5904 of the International Fire Code
- Storage areas and storage buildings for fireworks and explosives complying with Chapter 56 of the International Fire Code
502.8.1.1 System requirements
Exhaust ventilation systems shall comply with all of the following:
-
- The installation shall be in accordance with this code.
- Mechanical ventilation shall be provided at a rate of NOT LESS THAN 1 cfm per square foot [0.00508 m3/(sXm2)] of floor area over the storage area.
- The systems shall OPERATE CONTINUOUSLY unless alternate designs are approved.
- A MANUAL shutoff control shall be provided outside of the room in a position adjacent to the access door to the room or in another approved location. The switch shall be a break-glass or other approved type and SHALL BE LABELED: VENTILATION SYSTEM EMERGENCY SHUTOFF
- The exhaust ventilation shall be designed to consider the density of the potential fumes or vapors released. For fumes or vapors that are HEAVIER THAN AIR, exhaust shall be taken from a point within 12 inches (305 mm) of the floor. For fumes or vapors that are LIGHTER THAN AIR, exhaust shall be taken from a point within 12 inches (305 mm) of the highest point of the room.
- The location of BOTH the exhaust and inlet air openings shall be designed to provide air movement across ALL portions of the floor or room to prevent the accumulation of vapors.
- The exhaust air shall NOT be recirculated to occupied areas if the materials stored are capable of emitting hazardous vapors and contaminants have not been removed. Air contaminated with explosive or flammable vapors, fumes or dusts; flammable, highly toxic or toxic gases; or radioactive materials SHALL NOT BE RECIRCULATED.