The diffuser tank discussion continues and Peter Thomas, P.E. from Resource Compliance, Inc. was kind enough to offer us the following insight as to when a diffuser tank would be required. In most of my postings, I reference the International Fire Code (IFC) and International Mechanical Coden(IMC) quite often, but the Uniform Mechanical Code (UMC) is a code that I have very little experience with and as Peter points out, it is alive and well on the west coast. So it is worth noting that the Uniform Mechanical Code required Diffusion Tanks from 1994-2014 (the requirement removed in 2015 UMC)AND the UMC also required diffuser tanks be of steel construction. Most states utilize the International Mechanical Code, but select western states still use the UMC, or in the case of California the California Mechanical Code which is a derivative of the UMC. Here are some parts of the UMC that Peter provided:
2012 UMC §1120.0 Ammonia Discharge.
2012 UMC §1120.1 General.
Ammonia shall discharge into a tank of water that shall be used for no purpose except ammonia absorption. Not less than 1 gallon (4 L) of fresh water shall be provided for each pound (454 g) of ammonia that will be released in 1 hour from the largest relief device connected to the discharge pipe. The water used shall be prevented from freezing without the use of salt or chemicals. The tank shall be substantially constructed of not less than ⅛” (3.2 mm) or No. 10 MSG steel. The horizontal dimensions of the tank shall be equal to or less than one-half the height. The tank shall have a hinged cover or, where of the enclosed type, shall have a vent hole at the top. Pipe connections shall be through the top of the tank. The discharge pipe from the pressure-relief valves shall discharge ammonia in the center of the tank near the bottom but not more than 30 feet (9144 mm) below the surface of the water.
Exception: An ammonia-water absorption unit system installed outdoors serving a dwelling unit, provided the discharge is shielded and dispersed.
2009 UMC §1120.0 Ammonia Discharge.
Ammonia shall discharge into a tank of water that shall be used for no purpose except ammonia absorption. At least one (1) gallon (3.785 L) of fresh water shall be provided for each pound (454 g) of ammonia that will be released in one (1) hour from the largest relief device connected to the discharge pipe. The water used shall be prevented from freezing without the use of salt or chemicals. The tank shall be substantially constructed of not less than ⅛” (3.2 mm) or No. 10 MSG steel. The horizontal dimensions of the tank shall be equal to or less than one-half the height. The tank shall have a hinged cover or, if of the enclosed type, shall have a vent hole at the top. Pipe connections shall be through the top of the tank. The discharge pipe from the pressure-relief valves shall discharge ammonia in the center of the tank near the bottom but not more than thirty (30) feet (9,144 mm) below the surface of the water.
Exception: An ammonia-water absorption unit system installed outdoors serving a dwelling unit, provided the discharge is shielded and dispersed.
MAJOR CHANGE OCCURRED between 2006 and 2009 editions – in 2009 the code began requiring ONLY 1 gallon of water for each pound of ammonia that would be released in one (1) hour from the largest relief device connected to the discharge pipe. In the previous editions, the amount of water equaled the amount of NH3 in the process – one (1) gallon of FRESH water for each pound of NH3 in the process.
2006 UMC §1120.0 Ammonia Discharge.
Ammonia shall discharge into a tank of water that shall be used for no purpose except ammonia absorption. At least one (1) gallon (3.785 L) of fresh water shall be provided for each pound (454 g) of ammonia in the system. The water used shall be prevented from freezing without the use of salt or chemicals. The tank shall be substantially constructed of not less than 1/8 inch (3.2 mm) or No. 10 MSG steel. The horizontal dimensions of the tank shall be equal to or less than one-half the height. The tank shall have a hinged cover or, if of the enclosed type, shall have a vent hole at the top. Pipe connections shall be through the top of the tank. The discharge pipe from the pressure-relief valves shall discharge ammonia in the center of the tank near the bottom but not more than thirty (30) feet (9,144 mm) below the surface of the water.
Exception: An ammonia-water absorption unit system installed outdoors serving a dwelling unit, provided the discharge is shielded and dispersed.
2003 UMC §1120.0 Ammonia Discharge.
Ammonia shall discharge into a tank of water that shall be used for no purpose except ammonia absorption. At least one (1) gallon (3.785 L) of fresh water shall be provided for each pound (454 g) of ammonia in the system. The water used shall be prevented from freezing without the use of salt or chemicals. The tank shall be substantially constructed of not less than 1/8 inch (3.2 mm) or No. 10 MSG steel. The horizontal dimensions of the tank shall be equal to or less than one half the height. The tank shall have a hinged cover or, if of the enclosed type, shall have a vent hole at the top. Pipe connections shall be through the top of the tank. The discharge pipe from the pressure-relief valves shall discharge ammonia in the center of the tank near the bottom but not more than thirty (30) feet (9144 mm) below the surface of the water.
Exception: An ammonia-water absorption unit system installed outdoors serving a dwelling unit, provided the discharge is shielded and dispersed.
2000 UMC §1120.0 Ammonia Discharge
Ammonia shall discharge into a tank of water which shall be used for no purpose except ammonia absorption. At least one (1) gallon (3.785 L) of fresh water shall be provided for each pound (454 g) of ammonia in the system. The water used shall be prevented from freezing without the use of salt or chemicals. The tank shall be substantially constructed of not less than 1/8-inch (3.2 mm) or No. 10 M.S.G. steel. The horizontal dimensions of the tank shall be equal to or less than one half the height. The tank shall have a hinged cover or, if of the enclosed type, shall have a vent hole at the top. Pipe connections shall be through the top of the tank. The discharge pipe from the pressure-relief valves shall discharge ammonia in the center of the tank near the bottom but not more than thirty (30) feet (9144 mm) below the surface of the water.
Exception: An ammonia-water absorption unit system installed outdoors serving a dwelling unit provided the discharge is shielded and dispersed.
1997 UMC §1119 Ammonia Discharge
Ammonia systems shall be provided with an emergency discharge into a tank of water provided exclusively for ammonia absorption. At least 1 gallon (379 mL) of fresh water shall be provided for each pound (454 g) of ammonia in the system. The water used shall be prevented from freezing without the use of salt or chemicals. The tank shall be substantially constructed of not less than ⅛ in or No. 10 M.S.G. (2.51 mm) steel. The horizontal dimensions of the tank shall be equal to or less than one half of the height. The tank shall have a hinged cover or, if of the enclosed type, shall have a vent hole at the top. Pipe connections shall be through the top of the tank. The discharge pipe from the pressure-relief valves shall discharge ammonia in the center of the tank near the bottom but not more than 30 feet (9104 mm) below the surface of the water.
EXCEPTION: An emergency discharge is not required for ammonia-water absorption unit systems installed outdoors provided that the discharge is shielded and dispersed.
1994 UMC §1119 Ammonia Discharge
Ammonia systems shall be provided with an emergency discharge into a tank of water provided exclusively for ammonia absorption. At least 1 gallon (379 mL) of fresh water shall be provided for each pound (454 g) of ammonia in the system. The water used shall be prevented from freezing without the use of salt or chemicals. The tank shall be substantially constructed of not less than 1/8-inch or No. 10 M.S.G. (2.51 mm) steel. The horizontal dimensions of the tank shall be equal to or less than one half of the height. The tank shall have a hinged cover or, if of the enclosed type, shall have a vent hole at the top. Pipe connections shall be through the top of the tank. The discharge pipe from the pressure-relief valves shall discharge ammonia in the center of the tank near the bottom but not more than 30 feet (9104 mm) below the surface of the water.
EXCEPTION: An emergency discharge is not required for ammonia-water absorption unit systems installed outdoors serving a dwelling unit provided that the discharge is shielded and dispersed.