BigT:
obviously your ATF person is clueless....not unusal for the ATF
You will be required to get a variance from the ATf to place your Type 4 magazine in this shed of yours...
The first step is to download a MSDS sheet on Aerotech;s website and find out WHO your local fire dept marshall/head is and get in writing his ok... The ATf will NOT allow the variance unless your local AHJ (authority having jurisdiction, in this case youe local fire district Chief)
NFPA 1127: High Power Rocketry
This section deals with motors over 62.5 grams, here is the important stuff on storage requirements:
Section 4.19: Storage of High Power Rocket Motors, Motor Reloading Kits, and Pyrotechnic Modules.
4.19.1: High power rocket motors, motor reloading kits, and pyrotechnic modules shall be stored at least 7.6 m (25 ft) from smoking, open flames and other sources of heat.
4.19.2: Not more than 23 kg (50 pounds) of net propellant weight of high power rocket motors, motor reloading kits, and pyrotechnic modules subject to storage requirements of 27CFR 55 shall be stored in a Type 3 or Type 4 indoor magazine.
4.19.2.1: The indoor magazine shall be painted red and the top shall bear the following words in white letters at least 76mm (3 in) high: EXPLOSIVES KEEP FIRE AWAY
4.19.2.2: The indoor magazine shall not be located in a residence.
4.19.2.3: The indoor magazine shall be permitted to be located in a detached garage or out building.
4.19.2.4: The indoor magazine shall be permitted to be located in an attached garage of a single-family residence where approved by the authority having jurisdiction and the Bureau of Alcohol, Tobacco and Firearms.
https://www.atf.gov/alcohol/info/revrule/rules/2002-3.htm
ATF will approve variances to store explosives in a residence or dwelling only upon certain conditions including, but not limited to, receipt of a certification of compliance with State and local law, and documentation that local fire safety officials have received a copy of the certification
Notice 4.19.2.3 and 4.19.2.4
the "authority having jurisdiction(AHJ)" referenced here is your local Fire department fire chief.... There may be both city and county fire regulations....
Get your local AHJ to OK it and the Feds will also OK it....
Finally I would check State law to see if you might need to get a State Explosives Permit.....some states specifically denote that APCP is an explosive......So before you do Federal, you do Local, then State and then Federal.....
There are other Tenneess rocketeers in here that would know more about that ....
I just got through looking at the Tenneesse Code and I can find no references that APCP is considered an exploisve thus requiring any state explosives permit....
Tennessee is a NFPA1 state which means it adheres to the rules and regulations in NFPA 1122/1125 and 1127 .......Your State Fire Marshall is responsible for regulation of these......
You might also want to get a copy of NFPA 1127 from
https://www.nfpa.org for your own reference and knowledge...
good luck