Enclosed processing areas (vs. outside and open processing areas) that are handling/using the following, shall be ventilated at a rate sufficient to maintain the concentration of flammable vapors within the area at or below 25% of their lower flammable limit (LFL).
- Class I flammable liquids or as OSHA calls them Category 1/2 flammable liquids,
- Class II or Class III liquids or as OSHA calls them Category 3/4 flammable liquids when they are heated to temperatures AT OR ABOVE their flashpoints
These ventilation requirements are to be confirmed by one of the following:
- Calculations based on the anticipated fugitive emissions (see NFPA 30 Annex F for calculation method).
- A sampling of the actual vapor concentration under normal operating conditions.
- Sampling shall be conducted at a 5 ft radius from each potential vapor source extending to or toward the bottom and the top of the enclosed processing area.
- The vapor concentration used to determine the required ventilation rate shall be the highest measured concentration during the sampling procedure.
Although the code does NOT establish any testing frequencies for this ventilation flow, the annex does state:
Equipment in enclosed processing areas can deteriorate over time, and periodic evaluation should be conducted to ensure that leakage rates have not increased or that the ventilation rate is adequate for any increase in leakage rates.
We also have Chapter 6 where it states:
All fire protection equipment shall be properly maintained AND periodic inspections and tests shall be done in accordance with both standard practice and the equipment manufacturer’s recommendations.
The ventilation rate must be no less than 1 cubic foot per minute (CFM) of exhaust air for each square foot of floor area and this can be accomplished by using either a mechanical or natural/gravity means. The exhaust ventilation discharge(s) shall be to a safe location OUTSIDE the building.
Recirculation of the exhaust air is NOT recommended but is permitted. When the exhaust air is recirculated we MUST monitor it continuously using a fail-safe system that is designed to automatically:
- sound an alarm, AND
- stop recirculation, AND
- provide full exhaust to the outside in the event that vapor–air mixtures in concentrations over 25% of the lower flammable limit are detected
Now I am not quite sure why the code uses different language for this ventilation system design (vs the system for dispensing in storage areas), but in processing areas, the code merely states that provision shall be made for the introduction of make-up air in such a manner as to avoid short-circuiting the ventilation. Whereas the other design in section 18.6 clearly states how the FRESH Air/Make-up Air and Exhaust/Pick-up points are to be located to ensure we have a sweeping motion across the floor.
Ventilation shall be arranged to include all floor areas and pits where flammable vapors can collect.
The 2010 edition did finally settle the debate about room ventilation vs. local exhaust ventilation! Local exhaust ventilation (LEV) or spot ventilation to control special fire or health hazards, if provided, shall be permitted to be utilized for up to 75% of the required ventilation. So we CAN take credit for the airflow via our LEV systems, BUT PLEASE recognize the fact that many of these LEV systems have ON/OFF switches and may ONLY be used for specific periods of time for specific hazards. So be VERY CAREFUL counting the LEV airflows in establishing your 1 cfm of exhaust air for each square foot of floor area.
Where equipment such as dispensing stations, open centrifuges, plate and frame filters, and open vacuum filters is used in a building, the equipment and ventilation of the building shall be designed to limit flammable vapor–air mixtures under NORMAL OPERATING CONDITIONS to
- the interior of equipment and
- to not more than 5 ft from equipment that exposes Class I/CAT 1 and 2 liquids to the air
This means we have to ensure that not only do these pieces of processing equipment reduce our overall ventilation capabilities but that we actually have adequate air movement to ensure we can keep any flammable atmospheres INSIDE and within the processing equipment.