Ventilation requirements for flammable liquid storage areas where dispensing is conducted (NFPA 30, 2021)

Liquid storage areas where dispensing is conducted must have either a gravity ventilation system or a continuous mechanical exhaust ventilation system. If the dispensing involves Class I liquids (e.g. Category 1 & 2 liquids per OSHA terminology) mechanical ventilation is the ONLY acceptable option.  Regardless of the type used there are some FUNDAMENTAL requirements that NFPA has established in their 2021 edition of NFPA 30 – Flammable and Combustible Liquids Code.

First my cheat sheet on keeping NFPA’s Flammable Classes and OSHA’s Flammable Categories straight:

EXHAUST AIR is to be taken from a point near a wall on one (1) side of the room and within 12″ of the floor, with one (1) or more make-up inlets located on the opposite side of the room within 12″ of the floor. The locations of BOTH the exhaust and inlet air openings are intended to be on OPPOSITE sides of the room in order to ensure a “sweeping” air movement across ALL portions of the floor to prevent the accumulation of flammable vapors.

The “dirty air” (e.g. exhaust ventilation discharge) is to be discharged to a safe location outside the building.  This may sound like “common sense” but I have investigated an incident where the exhaust was discharged to the parking lot and the day of the spill, an employee was parked right in front of the discharge and when they started their car, ignition occurred.  The employee was parked in an identified parking spot!

I have written several articles over the years about the FRESH AIR make-up on the exhaust ventilation systems and how important this FRESH make-up air is to the system.  NFPA does allow for recirculation of the exhaust air, but ONLY when the ventilation is MONITORED CONTINUOUSLY using a fail-safe system that is designed to automatically:

1. sound an alarm, AND
2. stop recirculation, AND
3. provide full exhaust to the outside in the event that vapor-air mixtures in concentrations over 25% of the LEL/LFL are detected

If our ventilation system utilizes ducts to move either FRESH air or DIRTY air, these ducts MUST be dedicated to the flammable vapor ventilation system and not be used for any other purpose.  NFPA 30 also references NFPA 91-Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Particulate Solids for their design, installation, operation, and maintenance.

If our make-up air to the system is taken from within the building (NOT recommended – but allowed), the opening(s) MUST be equipped with a fire damper, as required in NFPA 91.  NOTE: I have had to use building air as my “fresh air” on some designs as the room/area the flammable dispensing did not have a “blank wall” and the roof was too littered with other HAZMAT vents such that we were concerned about our “fresh air” not being so “fresh”.  Thus management/client wanted to use “building air”.  KEEP IN MIND, what gets spilled/released in this area will be pulled into your flammable dispensing area, so there needs to be a thorough review of this area that will be supplying your “fresh make-up air” and then some serious CONTROL on what is allowed to be placed into this area.  If our system is a gravity system, the FRESH make-up air MUST be supplied from outside the building.

When we have chosen to use a mechanical ventilation system, it MUST provide at least 1 cfm of exhaust air for each square foot of floor area, but NEVER less than 150 cfm.  In other words, even in a small room, less than 150 square feet, the mechanical ventilation system must still provide at least 150 cfm.

And last but NOT LEAST, the mechanical ventilation system for dispensing areas MUST be equipped with an AIRFLOW SWITCH, or another equally reliable method, that is INTERLOCKED TO SOUND AN AUDIBLE ALARM upon failure of the ventilation system.