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  • NFPA
    NFPA 91: Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids
    Edition: 2004
    / user per year

Description of NFPA 91 2004


Prevent exhaust systems from spreading fire and increasing the risk of explosion!

NFPA 91 provides minimum requirements for the design, construction, installation, operation, testing, and maintenance of exhaust systems for air conveying of vapors, gases, mists, and noncombustible particulate solids except as modified or amplified by other applicable NFPA standards.

Changes to the 2004 edition include:

  • Expanded conditions under which flammable concentrations can exceed 25 percent of the lower flammable limit
  • Revised provisions for duct hanging and bracing design to account for both automatic sprinkler discharge as well as liquid cleaning solutions
  • A new provision allowing ductwork to be wrapped or encased to achieve the intended fire resistance rating.


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About NFPA

The mission of the international nonprofit NFPA, established in 1896, is to reduce the worldwide burden of fire and other hazards on the quality of life by providing and advocating consensus codes and standards, research, training, and education.


The world's leading advocate of fire prevention and an authoritative source on public safety, NFPA develops, publishes, and disseminates more than 300 consensus codes and standards intended to minimize the possibility and effects of fire and other risks.


NFPA membership totals more than 70,000 individuals around the world