In workplaces that handle/store hazardous materials, there is a need for exhaust ventilation systems when these “Control Areas” exceed the maximum allowable quantities (MAQ) of these hazardous materials. I have used the International Mechanical Code (IMC) as my baseline code for 20+ years. We see this code’s basic requirements in a lot of OSHA standards and other engineering standards for some specific HAZMATS such as NH3, Cl2, and flammables. Here are the seven (7) fundamentals of exhaust ventilation systems for hazardous materials.
General room/area exhaust ventilation systems should include all of the following to meet basic code requirements:
NOTE: I also discuss Local Exhaust Ventilation (LEV), Treatment Systems, and NFPA 30 requirements that go above basic IMC and IFC requirements.
1) Mechanical ventilation shall be provided at a rate of NOT LESS THAN 1 cfm per square foot of floor area over the storage area [0.00508 m3/(s⋅m2)].
This is the MINIMUM RATE for mechanical ventilation; however, it is important to note that the Safety Data Sheets (SDS) must be reviewed because the ventilation needed to maintain a safe environment could require a much higher airflow rate for certain materials. NOTE: NFPA 30 sets the minimum of 150 cfm regardless of room/area size. (see bottom of page)
2) The systems shall operate CONTINUOUSLY unless alternate designs are approved by the AHJ.
NOTE: NFPA 30 now requires an “alarm” on the system so to alert those in the area that the “continuous ventilation” has failed. See bottom of page for more on the NFPA design.
3) A MANUAL SHUTOFF CONTROL shall be provided OUTSIDE OF THE ROOM in a position adjacent to the access door to the room or in another approved location. The switch shall be a BREAK-GLASS OR OTHER APPROVED TYPE and shall be labeled: VENTILATION SYSTEM EMERGENCY SHUTOFF
An emergency shutoff must be installed at the entry door into the area and can be used to disable the ventilation system IN CASE OF A FIRE.
4) The exhaust ventilation shall be designed to consider the density of the potential fumes or vapors released.
- For fumes or vapors that are HEAVIER THAN AIR, exhaust shall be taken from a point WITHIN 12 INCHES OF THE FLOOR.
- For fumes or vapors that are LIGHTER THAN AIR, exhaust shall be taken from a point WITHIN 12 INCHES OF THE HIGHEST POINT OF THE ROOM.
5) The location of both the exhaust and inlet air openings shall be designed to PROVIDE AIR MOVEMENT ACROSS ALL PORTIONS OF THE FLOOR OR ROOM to prevent the accumulation of vapors.
The system must move air across all of the area being protected to prevent the accumulation of vapors in isolated “DEAD” SPOTS in the room.
6) The EXHAUST AIR SHALL NOT BE RECIRCULATED to OCCUPIED AREAS if the materials stored are CAPABLE OF EMITTING HAZARDOUS VAPORS and CONTAMINANTS HAVE NOT BEEN REMOVED.
7) Air contaminated with EXPLOSIVE or FLAMMABLE vapors, fumes, or dusts; FLAMMABLE, HIGHLY TOXIC OR TOXIC GASES; or RADIOACTIVE MATERIALS shall NOT BE RECIRCULATED.
Hazardous vapors must not be recirculated back into the storage room or to any other portion of the building. This requirement prevents the buildup of vapors over time to hazardous levels and also prevents contamination of other areas.
Local Exhaust Ventilation (LEV)
Where gases, liquids, or solids in amounts exceeding the MAQ per control area AND having an NFPA 704 hazard ranking of 3 or 4 are DISPENSED OR USED, mechanical exhaust ventilation shall be provided to CAPTURE GASES, FUMES, MISTS OR VAPORS AT THE POINT OF GENERATION.
Exception: Where it can be demonstrated that the gases, liquids, or solids do not create harmful gases, fumes, mists, or vapors.
The intent of LEV is to ensure that hazardous vapors and fumes are captured and exhausted at the point where the materials are being generated rather than allowing them to disperse into the room where occupants could be exposed to the harmful effects. LEV is required ONLY where the materials have an NFPA 704 hazard ranking of 3 or 4 AND ALSO exceed the MAQ for the control area.
The LEV requirements would apply to:
- Corrosives exceeding the maximum allowable quantity per control area are dispensed or used
- Indoor areas where cryogenic fluids in ANY QUANTITY are dispensed, except where it can be demonstrated that the cryogenic fluids do not create harmful vapors
-
the use, dispensing and mixing of flammable and combustible liquids in open or closed systems in amounts exceeding the MAQ per control area and for bulk transfer and process transfer operations when natural ventilation is NOT effective for the materials used, dispensed, or mixed
Treatment Systems
A treatment system is necessary when we have INDOOR AND OUTDOOR STORAGE AND USE of HIGHLY TOXIC and TOXIC LIQUIDS in amounts exceeding the MAQ per control area.
Exhaust scrubbers or other systems for processing vapors of HIGHLY TOXIC LIQUIDS shall be provided where a spill or accidental release of such liquids can be expected to release highly toxic vapors at NORMAL TEMPERATURE AND PRESSURE.
Because of the dangers associated with the potential vapors created by an accidental release or spill of highly toxic liquids in amounts exceeding the MAQ, both the IFC and the IMC require that storage and use areas, both indoors and outdoors, have an exhaust scrubber or similar system installed to process released vapors. Such systems are termed treatment systems and are to be designed, constructed, and installed in accordance with the IFC, specifically Section 6004.2.2.7. This requirement is specific to HIGHLY TOXIC LIQUIDS and would require a treatment system to collect and process any vapors that might escape if a spill should occur at “normal temperature and pressure.”
In other words, vapors would not be highly toxic at normal temperature and pressure conditions, a treatment system would NOT be required. The focus of this section is on the inhalation hazards associated with highly toxic materials. Material may be considered highly toxic by:
- skin contact, or
- ingestion,
- but NOT create an inhalation hazard because of the low volatility of the liquid
I have received a lot of questions about the NFPA 30 ventilation requirements from my PSM readers, as many of them have adopted NFPA 30 as their baseline RAGAGEP for their flammable liquids process(s). Here you go…
(emphasis by me)
A couple of key points:
- NFPA has much stricter requirements for “recirculated air”
- NFPA requires an alarm on the ventilation system
18.6 Ventilation for Dispensing Areas.
Liquid storage areas where dispensing is conducted shall be provided with either a GRAVITY SYSTEM or a CONTINUOUS MECHANICAL EXHAUST ventilation system. Mechanical ventilation shall be used if Class I liquids are dispensed within the room.
(SAFTENG NOTE: NFPA’s Class 1A, 1B, and 1C’s are the same as OSHA’s CAT 1, 2, and 3’s with FPs<100ºF)
18.6.1 Exhaust air shall be taken from a point near a wall on one side of the room and within 12 in. (300 mm) of the floor, with one or more make-up inlets located on the opposite side of the room within 12 in. (300 mm) of the floor.
18.6.2 The location of both the exhaust and inlet air openings shall be arranged to provide air movement across all portions of the floor to prevent accumulation of flammable vapors.
18.6.3 * Exhaust ventilation discharge shall be to a safe location outside the building.
18.6.3.1 Recirculation of the exhaust air shall be permitted only when it is monitored continuously using a fail-safe system that is designed to automatically sound an alarm, stop recirculation, and provide full exhaust to the outside in the event that vapor-air mixtures in concentrations over one-fourth of the lower flammable limit are detected.
18.6.4 If ducts are used, they shall not be used for any other purpose and shall comply with NFPA 91.
18.6.4.1 If make-up air to a mechanical system is taken from within the building, the opening shall be equipped with a fire door or damper, as required in NFPA 91.
18.6.4.2 For gravity systems, the make-up air shall be supplied from outside the building.
18.6.5 Mechanical ventilation systems shall provide at least 1 cfm of exhaust air for each square foot of floor area (0.3 m3/min/m2), but not less than 150 cfm (4 m3/min).
18.6.5.1 The mechanical ventilation system for dispensing areas shall be equipped with an airflow switch or other equally reliable method that is interlocked to sound an audible alarm upon failure of the ventilation system.