Ind. Admin. Code tit. 355, r. 3-9-1 – Minimum rate of discharge for pressure relief valves

Sec. 1. The minimum required rate of discharge in cubic feet per minute of air at one hundred twenty percent (120%) of the maximum permitted start-to-discharge pressure for pressure relief valves to be used on containers other than those constructed in accordance with DOT specifications shall be as follows:

Surface Area	Flow Rate
Square Feet	CFM Air
20	258
25	310
30	360
35	408
40	455
45	501
50	547
55	591
60	635
65	678
70	720
75	762
80	804
85	845
90	885
95	925
100	965
105	1,010
110	1,050
115	1,090
120	1,120
125	1,160
130	1,200
135	1,240
140	1,280
145	1,310
150	1,350
155	1,390
160	1,420
165	1,460
170	1,500
175	1,530
180	1,570
185	1,600
190	1,640
195	1,670
200	1,710
210	1,780
220	1,850
230	1,920
240	1,980
250	2,050
260	2,120
270	2,180
280	2,250
290	2,320
300	2,380
310	2,450
320	2,510
330	2,570
340	2,640
350	2,700
360	2,760
370	2,830
380	2,890
390	2,950
400	3,010
450	3,320
500	3,620
550	3,910
600	4,200
650	4,480
700	4,760
750	5,040
800	5,300
850	5,590
900	5,850
950	6,120
1,000	6,380
1,050	6,640
1,100	6,900
1,150	7,160
1,200	7,400
1,250	7,660
1,300	7,910
1,350	8,160
1,400	8,410
1,450	8,650
1,500	8,900
1,550	9,140
1,600	9,380
1,650	9,620
1,700	9,860
1,750	10,090
1,800	10,330
1,850	10,560
1,900	10,800
1,950	11,030
2,000	11,260
2,050	11,490
2,100	11,720
2,150	11,950
2,200	12,180
2,250	12,400
2,300	12,630
2,350	12,850
2,400	13,080
2,450	13,300
2,500	13,520

(1) Surface Area = Total outside surface area of a container in square feet. When the surface area is not stamped on the name plate or when the marking is not legible, the area can be calculated by using one (1) of the following formulas:
1. (A) Cylindrical container with hemispherical heads:
  1. Area = overall length in feet times outside diameter in feet times 3.1416
2. (B) Cylindrical container with other than hemispherical heads:
  1. Area = (overall length in feet plus 0.3 outside diameter in feet) times outside diameter in feet times 3.1416
3. (C) Spherical container:
  1. Area = outside diameter in feet squared times 3.1416
(2) Flow Rate CFM Air = Cubic feet per minute of air required at standard conditions, sixty (60) degrees Fahrenheit and atmospheric pressure (14.7 psia).

The rate of discharge may be interpolated for intermediate values of surface area. For containers with a total outside surface area greater than two thousand five hundred (2,500) square feet, the required flow rate can be calculated using the formula, Flow Rate CFM Air = 22.11 A^0.82, where A = outside surface area of the container in square feet.

(State Chemist of the State of Indiana; Agricultural Ammonia App A; filed Dec 30, 1965, 2:15 p.m.: Rules and Regs. 1966, p. 26; filed Jan 19, 2001, 2:04 p.m.: 24 IR 1648; errata filed Apr 24, 2001, 9:06 a.m.: 24 IR 2709; readopted filed Jun 20, 2001, 3:22 p.m.: 24 IR 3822; readopted filed Apr 27, 2007, 2:03 p.m.: 20070509-IR-355070039RFA; readopted filed Nov 25, 2013, 3:27 p.m.: 20131225-IR-355130482RFA; readopted filed Jul 2, 2019, 10:42 a.m.: 20190731-IR-355190258RFA; readopted filed Nov 4, 2025, 2:37 p.m.: 20251119-IR-355240619RFA)