We continue to see the “check the box” engineering when it comes to “ventilation” requirements for processes that fall under PSM/RMP. I have written about the design basis and the many flaws we come across regarding the actual design, but this one is becoming more and more prevalent. I am thinking “space” is becoming less available so facilities are installing their FRESH AIR INTAKES in the darnedest places. In this article, I home to educate those interested in the most basic need for a FRESH AIR INTAKE and that is…. FRESH AIR.
Many RAGAGEPs associated with the handling, storage and processing of Highly Hazardous Chemicals (HHC) or as EPA calls them Extremely Hazardous Substances (EHS) require “ventilation”, whether it be to control flammable atmospheres or to reduce exposure to toxic atmospheres. In large process areas that are enclosed, these enclosures are ventilated by removing the contaminated air and replacing it with FRESH AIR. This fresh air make-up is an ABSOLUTE CRITICAL path for the ventilation to work as it is designed. It is not that uncommon to find some enclosed areas with exhaust fans sized properly – BUT NO FRESH AIR make up available, so the fans are basically sucking in air from where ever they can – this is NOT a controlled system. We want the air pattern inside the enclosed area to be a sweeping motion so that we can ventilate the entire space, leaving NO POCKETS of hazardous atmospheres and we want the air that is doing the sweeping to be FRESH AIR. So the location of the fans in relation to the location(s) of the FRESH AIR intakes is CRITICAL as well. But this article is about where the FRESH AIR intakes can/should be located and where they cannot be located.
Most of the RAGAGEPs that call for ventilation will state that the “intakes” supply “fresh air”. They do not go into details about where these intakes can be located so as to leave some flexibility for the user. But we can find some BASELINE guidance that very well may be “CODE” for some processes. The International Mechanical Code (IMC) does, in fact, have some limitations on how and where the FRESH AIR intakes can be located; keeping in mind that many jurisdictions may have adopted this “code” making it an ABSOLUTE requirement regardless of PSM/RMP coverage (e.g. even those processes under the PSM/RMP thresholds). Here is what the IMC 2012 states about the FRSH AIR INTAKES:
Chapter 4 – Ventilation
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401.4 Intake opening location.
Air intake openings shall comply with all of the following:
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- Intake openings shall be located a minimum of 10 feet (3048 mm) from lot lines or buildings on the same lot.
- Mechanical and gravity outdoor air intake openings shall be located not less than 10 feet (3048 mm) horizontally from any hazardous or noxious contaminant sources, such as vents, streets, alleys, parking lots and loading docks, except as specified in Item 3 or Section 501.2.1. Outdoor air intake openings shall be permitted to be located less than 10 feet (3048 mm) horizontally from streets, alleys, parking lots, and loading docks provided that the openings are located not less than 25 feet (7620 mm) vertically above such locations. Where openings front on a street or public way, the distance shall be measured from the closest edge of the street or public way.
- Intake openings shall be located not less than 3 feet (914 mm) below contaminant sources where such sources are located within 10 feet (3048 mm) of the opening.
- Intake openings on structures in flood hazard areas shall be at or above the elevation required by Section 1612 of the International Building Code for utilities and attendant equipment.
So basically this part of the IMC is regulating the locations of our FRESH AIR intakes so as to ensure the air being pulled into the ventilation system is indeed FRESH AIR. One of the most basic failures we continue to see, even on brand new processes, is that the fresh air intakes are pulling air from an area that houses the HHC. In many cases, the air is being pulled from the bulk storage area for the HHC. In these cases, we can easily come up with a leak scenario OUTSIDE the enclosed area and the ventilation will actually pull the leaked HHC into the enclosed area. Some of these ventilation systems operate continually and when an HHC is recognized by the fixed monitors the ventilation will kick into EMERGENCY MODE which will actually pull in more of the HHC; this is all happening inside an enclosed space where the ventilation is designed to REMOVE the HHC/EHS – NOT introduce it to the enclosed space!.
So when we design our ventilation system(s) that requires a FRESH AIR intake, we may want to ensure our designer considers where the FRESH AIR intake is located, as well as its size! The IMC is a good start if your chosen ventilation RAGAGEP does not provide guidance as to the location of your FRESH AIR intake; but by all means, do NOT place your largest source of your HHC directly in front of your FRESH AIR intake(s).