When we have a hazardous material that poses either a physical hazard such as a flash fire/explosion or a health hazard we need to manage this hazard using our hierarchy of controls. The first control is to see if we can use a “safer alternative” which we call “Elimination/Substitution”. But if this is not possible we go to our next layer – Engineering Control(s) and the most popular engineering control for a gas/vapor/fume is some type of ventilation system, most commonly used are Local Exhaust Ventilation (LEV) or ventilating the entire room. But when it comes to the design of these ventilation systems we have seen some real head-scratchers! In the world of Process Safety, we are required to have a “Ventilation system design” (1910.119(d)(3)(i)(E) that documents the system meets the needs of the process area/room/building. This article is for those ventilation systems NOT necessarily associated with a PSM/RMP covered process, although many of the requirements discussed will be applicable to a PSM/RMP ventilation system. This article is more in-line with operators handling HAZMATs in their production area and the ventilation is intended to manage the hazardous gas/vapors/fumes generated from their work.
For this article, I am using the International Mechanical Code (IMC) and the International Fire Code (IFC) as they are my favorite codes for these ventilation systems. They are also the codes that were used in almost all of my plants throughout my career in the chemical and semiconductor industries. The sections of the IMC that are most applicable are Sections 501 and 510, but where other sections have critical requirements I include as well. I have listed some sections below just to indicate that the IMC has several process/industry-specific ventilation design requirements. So let’s begin with Section 501 GENERAL…