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.