Emergency vents that I currently see with new tanks for such product as fuel oil are manhole covers fitted with long threaded bolts allowing about 1/2" travel for the cover to lift.

Depending on the roof construction and the code of construction, they may have had frangible roofs rather than emergency vents.  It's also possible they were built for products not requiring emergency venting.

the tanks are horizontal tanks with no blow-off roof and no emergency vent manways or other forms of emergency vents.  the only thing that might count for e-vent is if the 3" operational vent were to be considered.  This 3" vent has it's own complications in that they have a floating level gauge in it as well.

i guess the big question is how stable does a product have to be to not require emergency venting and does that limit live within the "0" or the "1" NFPA signage rating.

thanks for the quick response you two... i've more or less been on vacation since the post and haven't thought much about it.

Darth..

Study up on NFPA-30 and understand the differences between the various categories of flammable liquids. Emeregency vents are required for certain types of liquids.

Additionally, consider the method of offloading the liquids you intend to store in the tanks. If the tanks are being filled by tanker trucks with an "air pad" (trucks that use air pressure to offload).

In that case, an emergency vent is POSITIVELY required. FRP/plastic tanks have been known to fail due to the pressure surge that occurs at the end of delivery.

   

Why take a chance? Do the API 2000 calcs. based on hepthane and install the emergency vent (for these small tanks, the EV's won't have to be very large). If you consider the alternate circumstances, it's not worth risk.

PS - tanks this small can not be considered having frangible roofs.

okay... so i managed to stay away from purchasing NFPA codes over the years (always too busy with the API and STI standards which are more applicable for existing tanks.  also, since all the other times i've seen ASTs without E-vents they were always holding very flammable product and were no-brainers that they would have to install) but i finally broke down and got one like MJCronin suggested... i've copy pasted an interesting portion that addresses this question.

appears to me that the tanks that are greater than 12000 gallons didn't need e-venting.(the big ones actually were 15000 not the 12000 that i threw out there in a previous post.) also worth noting, all the tanks in the containment area hold the same product.

Class IIIB liquids are flash point over 200F... which translates to 1 on the NFPA 704 hazard sign.   Side note....I bet i'm not the 1st person to think it's foolish for the NFPA to classify stable materials as "1" according to one standard and highly volatile materials as I (aka 1) according to another standard.


"22.7 Emergency Relief Venting for Fire Exposure for Aboveground
Storage Tanks.
22.7.1 General.
22.7.1.1 Every aboveground storage tank shall have emergency
relief venting in the form of construction or a device or
devices that will relieve excessive internal pressure caused by
an exposure fire.
22.7.1.1.1 This requirement shall apply to each compartment
of a compartmented tank, the interstitial space (annulus) of a
secondary containment–type tank, and the enclosed space of
tanks of closed-top dike construction.
22.7.1.1.2 This requirement shall also apply to spaces or enclosed
volumes, such as those intended for insulation, membranes,
or weather shields, that are capable of containing liquid
because of a leak from the primary vessel. The insulation,
membrane, or weather shield shall not interfere with emergency
venting.
22.7.1.1.3 Tanks storing Class IIIB liquids that are larger than
12,000 gal (45,400 L) capacity and are not within the diked
area or the drainage path of tanks storing Class I or Class II
liquids shall not be required to meet the requirements of
22.7.1.1."

There are some overfill prevention devices currently installed on some large flange connections which could be switched out for e-vents or possibly long-bolted for the smaller tanks.  I'm thinking i'll recommend they consider configuring those sensors to have a lifting top-plate for a base for the sub-12000 gallon tanks.
  

Darth.....

I think that your post touches on the issues/problems related to the multiple usage of tanks in the US.

In other parts of the world, a tank has the flamablity/usage "rating" noted on the design drawings.(And on the tank) If you want to use it for something else, you must change the fire rated class AND CHANGE THE DRAWINGS!!!

(A watertank is a watertank is a ....apologies to Gertrude Stein)

But, in the USA, we have these generic containers that can be used for multiple services.......just get some PE to take responsibility and sign things of when the Fire Inspector comes by......and every thing will be OK