Is the required venting area equation and calculation in nfpa 68 2007 different then the required area for venting that may have been made by the previous nfpa 68 edition. Sulfur pit explosion protection nfpa 68 interpretation. In principle modeling developed for gas explosions venting should also apply to dust explosion. Dust explosion standards european, astm and nfpa standards. Nfpa 68 calculations to determine pred reduced pressure with explosion vents, indoor flameless venting, building venting panels and weak shell construction. Reflecting changes in technology, recent fire experience, and current fire safety practices, nfpa 68 standard on explosion protection by deflagration venting applies to the design, location, installation, maintenance, and use of devices and systems that vent. With only one vent, enter the longest distance from one end of the vessel to the opposite end of the vent. En standard en14491 and nfpa 68 provide detailed guidance on the process of vent area calculation and vent system design, refer to shapa technical bulletin no. Nfpa 30 emergecny vent tank blanketing and venting. Nfpa and the nfpa logos are trademarks and service marks of nfpa. Nfpa 68 north america and en 14491 europe guidelines.
Nfpa 68 standard on explosion protection by deflagration venting, 2007. Nfpa 68 vent sizing dust explosions nfpa 68 venting devices nfpa 69 explosion resistant products nfpa 69 explosion isolation 3. Nfpa 68, standard on explosion protection by deflagration venting, was first. Calculating p red and the derivative parameters and stepping through the nfpa 68 procedure yields a required vent area a v of 198footsquare, or 48% of the wall area, an undesirably large area.
Nfpa 68 pstat, pred, and pes relationships nfpa fire. The current graphs represent the previous dust methodology. The required vent area of the explosion vents are described by calculations found in nfpa 68. Replace the published graphs with these new graphs so that results are consistent with the equations. We need to determine the vent area and verify the enclosure strength is adequate. January 2426, 2017, courtyard charleston historic district, charleston, sc, courtyard charleston historic district. Nfpa 68 specifies what explosion venting must do to meet standards. To calculate vent area size, the recommendations given in european standard en 14491. Dust explosion protection using flameless venting fike. Nfpa standards are reproduced with nfpa s permission by.
For more information, see the later section how nfpa 68. There are conflicts with the referenced nfpa 68 venting of deflagrations, in the method of determining the vent size, the recommended maximum mass of the vent. I have a problem to calculate the av3 area of dust collector vents due to the effects of inertia using nfpa 68 standard. Explosion vent area calculations sizing cmc technologies is able to provide preliminary calculations for isolated enclosures according to en 14491. Standard on explosion protection by deflagration venting this standard applies to the design, location, installation, maintenance, and use of devices and systems that vent the combustion gases and. The vent sizing equations in nfpa 68 are based on test data, primarily from great britain and germany, which has been updated and refined for over 30 years. It is the personal work of samuel rodgers, given freely without any implied warranty or guarantee. P red means the maximum pressure in the vented enclosure during the explosion. Explosion protection by deflagration venting through nfpa.
Guide for venting of deflagrations, 1998 nfpa standards are of national fire protection association nfpa. The 20 edition of nfpa 68 standard on explosion protection by deflagration venting will replace vent area sizing equations containing the gas deflagration index, k g, for highpressure applications with equations containing the laminar burning velocity, s u. This is a spreadsheet which is free to use on the nfpa website. Excel spreadsheet for calculating explosion venting lev. I am working on a sulfur pit, using an inpit degassing technology. The inertial factor was developed from the fm vent calculation methodology which they graciously gave to the world, with special information provided to the 68 committee. Although the new equation produces lower p red results compared to earlier nfpa 68 editions, there still can be significant increases in p red with the addition of a vent.
En14491, except when the silos had a lengthdiameter ratio of 1. Dust explosion venting of silos process protection. Comparisons are made between the vent areas used in largescale experiments and the vent areas calculated by the nfpa 68 and en14491 equations for the reduced pressures measured in the experiments. Nfpa 68 gives formulas to calculate the exact size of an explosion relief vent. I was recently given the calculation for emergency venting as per nfpa 30 using a manhole with long bolts as per the below.
Nfpa 68 discusses explosion venting for a broad range of building occupancies and equipment. In general, nfpa 68 2018 details a heap of considerations in relation to deflagration vents, including their design, location, installation, maintenance, and use, so that they can vent combustion gases and pressures resulting from a deflagration within an enclosure to minimize damage. In both nfpa 68 and en 14491, the equation used to calculate the minimum necessary vent area of dust is used for a hybrid mixture. Step 3 calculate wetted area if the tank size is not on either chart, wetted area can be calculated. The correlations for calculating the vent area a v for gas and dust explosions in highstrength enclosures included in nfpa 68, en 14994 and en 14991 have been derived by bartknecht 1993. It contains the most detailed standards and calculations. Modified swiftepstein equations replace both gas venting equations in previous editions of nfpa 68. Nfpa 68 gives formulas to calculate the exact size of an explosion relief vent for dust collectors. The equation for determining vent area for elevated or.
Nfpa 86 ovens and furnaces, provides recommended venting ratios and other guidance with reference to nfpa 68 venting of deflagrations. Article five ways new explosion venting requirements for. The vent selection chapter includes venting capacities of specific morrison vents. In the absence of an official performance standard, compliance with nfpa 68 and the. A v vent area m2 c venting parameter a s internal surface area of enclosure m2 p red maximum pressure developed in a vented enclosure during a vented deflagration bar note. Structure magazine when structural blast design doesnt. Vent areas calculated according to nfpa 68 were smaller than those calculated in line with. Under nfpa 68 guidelines the minimum required vent area for lowstrength enclosures is determined by the following equation. In 1974, nfpa 68 was revised, and the work done in great britain and germany was included with the hope that the new information would provide a means for calculating vent ratios with a greater degree. This free area calculator determines the area of a number of common shapes using both metric units and us customary units of length, including rectangle, triangle, trapezoid, circle, sector, ellipse, and parallelogram. Sulfur pit explosion protection nfpa 68 interpretation posted in relief devices forum. Standard on explosion protection by deflagration venting covers the. The documents or portions thereof listed in this chapter are referenced within this standard and shall be considered part of the requirements of this document.
The venting capacity charts and wetted area tables were taken directly from nfpa 30 and ul 142. Mectric technical publication 0817 nfpa 68 explosion protectionexplosion vents page 2 of 2 as the formula specifies, if pstat, kst, v volume of vessel dirty volume for dust or pmax increase, vent area increases. Finite element analysis to determine pes enclosure strength as required by nfpa 68. An explosion vent for your dust collector acts in a similar way. Increase the vent relief area to com pensate for the effects of.
A revised equation helps you determine vent area for elevated or subatmospheric pressure, with an example calculation added to the annex. As pred the pressure value the end user provides relating to their vessel maximum allowable pressure decreases, vent. Calculate the vent area for each section of the enclosure or for the whole enclosure diameter the effective area, a eff, shall be determined by dividing v eff by h based on the longest central axis flame length. The required relief area necessary to protect plant or equipment may be determined by using the most current standards of nfpa 68. Errata nfpa 68 national fire protection association. Nfpa 68 for dust collector explosion venting cardinal. Both nfpa and factory mutual use this value in formulas to calculate the amount of explosion vent area re quired for a dust collector. This standard applies to the design, location, installation, maintenance, and use of devices and systems that vent the combustion gases and pressures resulting from a deflagration. Excel spreadsheet for calculating explosion venting this is a spreadsheet which is free to use on the nfpa website. There are no basic conflicts in fm 69 with nfpa 86 ovens and furnaces.
Venting calculations to determine the net free ventilating area of a vent, divide the gross ventilating do not include metal frame edges area by the area factor below. Excel spreadsheet for calculating explosion venting. Explosion vent compliance with nfpa 68 kernic systems. Determination of vent area sizes and explosion pressures. Standard on explosion protection by deflagration venting.