Anhydrous Ammonia unloading design specs in 1910.111

This article is being posted in my Hazardous Materials section rather than the Process Safety section because the vast majority of my finds regarding the lack of proper design are almost exclusively in processes that have less than 10,000 pounds. I am hoping that those who read this will understand that what I am going to discuss in this article has absolutely nothing to do with being a PSM/RMP covered process and everything to do with basic compliance and safety regarding Anhydrous Ammonia (NH3).

Without a doubt, in my opinion, the biggest risk these facilities face is the unloading of NH3 from a tank truck to their bulk storage tanks. And I am not the only one who believes this is the biggest risks, as OSHA, ANSI and the Compressed Gas Association (CGA) have specific unloading system design requirements; however, this article will only discuss the requirements in 1910.111.

For those processes that are UNDER the PSM/RMP TQ, they will be required to meet:

(emphasis by me)

1910.111(b) Basic rules

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1910.111(b)(8) Hose specifications.

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1910.111(b)(8)(iv) Where hose is to be used for transferring liquid from one container to another, “wet” hose is recommended. Such hose SHALL be EQUIPPED WITH APPROVED shutoff valves at the discharge end. Provision shall be made to prevent excessive pressure in the hose.

1910.111(b)(12) Transfer of liquids

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1910.111(b)(12)(vii) Loading and unloading systems shall be protected by suitable devices to PREVENT EMPTYING OF THE STORAGE CONTAINER OR THE CONTAINER BEING LOADED OR UNLOADED in the event of severance of the hose. BACKFLOW CHECK VALVES or PROPERLY SIZED EXCESS FLOW VALVES shall be installed where necessary to provide such protection. In the event that such valves are not practical, REMOTELY OPERATED SHUTOFF VALVES MAY BE INSTALLED.

1910.111(c) Systems utilizing STATIONARY, NONREFRIGERATED STORAGE CONTAINERS

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1910.111(c)(2) Container valves and accessories, filling and discharge connections

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1910.111(c)(2)(i) Each FILLING CONNECTION shall be provided with a COMBINATION back-pressure check valve AND excess-flow valve; one double or two single back-pressure check valves; or a positive shutoff valve in conjunction with either an internal back-pressure check valve or an internal excess flow valve.

So it is clear, that 1910.111(b)(12)(vii) allows for either:

Backflow check valves, or
properly sized excess flow valves

However, we get to paragraph (c) and it applies to Systems utilizing stationary, non-refrigerated storage containers, we see there are additional controls required. This paragraph applies to stationary, non-refrigerated storage installations utilizing containers other than those covered in paragraph (e) of this section [DOT containers such as Nurse Tanks]. Paragraph (b) of this section [Basic rules] applies to this paragraph unless otherwise noted.

(c)(2)(i) requires that EACH FILLING CONNECTION shall be provided with:

a combination back-pressure check valve AND excess-flow valve;
one (1) double or two (2) single back-pressure check valves; or
a positive shutoff valve in conjunction with either:
1. an internal back-pressure check valve, or
2. an internal excess flow valve

So we can see there are several options and some involve the use of excess flow valves (EFV); however, in many cases, we see piping designs that would nullify the EFV. The standard states the flowing about the sizing of the EFVs and the pipe sizes downstream:

1910.111(b)(6)(iii) Excess flow valves where required by these standards shall close automatically at the rated flows of vapor or liquid as specified by the manufacturer. The connections and line including valves and fittings being protected by an excess flow valve shall have a GREATER CAPACITY THAN THE RATED FLOW OF THE EXCESS FLOW VALVE so that the valve will close in case of failure of the line or fittings.

This means that if we have a 2″ EFV and downstream we have a 3/4″ pipe, if the 3/4″ pipe fails – the flow will NOT be sufficient to “trip” the EFV. And with NO OTHER means of protection, we could drain the entire tank

NOTE: the standard does an excellent job explaining what “approved” means when it comes to using equipment…

1910.111(b)(1) Approval of equipment and systems. Each appurtenance shall be approved in accordance with paragraph (b)(1) (i), (ii), (iii), or (iv) of this section.

1910.111(b)(1)(i) It was installed before February 8, 1973, and was approved, tested, and installed in accordance with either the provisions of the American National Standard for the Storage and Handling of Anhydrous Ammonia, K61.1, or the Fertilizer Institute Standards for the Storage and Handling of Agricultural Anhydrous Ammonia, M-1, (both of which are incorporated by reference as specified in § 1910.6) in effect at the time of installation; or

1910.111(b)(1)(ii) It is accepted, or certified, or listed, or labeled, or otherwise determined to be safe by a nationally recognized testing laboratory; or

1910.111(b)(1)(iii) It is a type which no nationally recognized testing laboratory does, or will undertake to, accept, certify, list, label, or determine to be safe; and such equipment is inspected or tested by any Federal, State, municipal, or other local authority responsible for enforcing occupational safety provisions of a Federal, State, municipal or other local law, code, or regulation pertaining to the storage, handling, transport, and use of anhydrous ammonia, and found to be in compliance with either the provisions of the American National Standard for the Storage and Handling of Anhydrous Ammonia, K61.1, or the Fertilizer Institute Standards for the Storage and Handling of Agricultural Anhydrous Ammonia, M-1, in effect at the time of installation; or

1910.111(b)(1)(iv) It is a custom-designed and custom-built unit, which no nationally recognized testing laboratory, or Federal, State, municipal or local authority responsible for the enforcement of a Federal, State, municipal, or local law, code or regulation pertaining to the storage, transportation and use of anhydrous ammonia is willing to undertake to accept, certify, list, label or determine to be safe, and the employer has on file a document attesting to its safe condition following the conduct of appropriate tests. The document shall be signed by a registered professional engineer or other person having special training or experience sufficient to permit him to form an opinion as to safety of the unit involved. The document shall set forth the test bases, test data and results, and also the qualifications of the certifying person.

1910.111(b)(1)(v) For the purposes of this paragraph (b)(1), the word “listed” means that equipment is of a kind mentioned in a list which is published by a nationally recognized laboratory which makes periodic inspection of the production of such equipment, and states such equipment meets nationally recognized standards or has been tested and found safe for use in a specified manner. “Labeled” means there is attached to it a label, symbol, or other identifying mark of a nationally recognized testing laboratory which, makes periodic inspections of the production of such equipment, and whose labeling indicates compliance with nationally recognized standards or tests to determine safe use in a specified manner. “Certified” means it has been tested and found by a nationally recognized testing laboratory to meet nationally recognized standards or to be safe for use in a specified manner, or is of a kind whose production is periodically inspected by a nationally recognized testing laboratory, and it bears a label, tag, or other record of certification.

1910.111(b)(1)(vi) For the purposes of this paragraph (b)(1), refer to 1910.7 for the definition of a nationally recognized testing laboratory.

The standard mentions “Back Pressure Check Valves” and “Double Check Valves“ so I thought I would explain what these valves are. The Back Pressure Check Valves are NORMALLY CLOSED valves. The check mechanism is spring-loaded to hold the valve in the closed position at any orientation and precludes the possibility of flow out of the container. When the flow starts into the container, pressure overcomes the spring force and opens the check. As soon as flow stops or reverses, the check closes. The action prevents the escape of tank contents in the event of accidental breakage of the piping or fittings leading to the container opening. These check valves may also be installed in piping where flow must be limited to one direction.

Double Check Valves are essentially two (2) single check valves assembled within one (1) body and furnished with four (4) test cocks and two (2) shut-off valves.

LASTLY, if you’re interested in comparing 1910.111 to ANSI K61.1, here are the requirements of K61.1:

Suitable back-flow check valves in LOADING LINES for non-refrigerated containers
Suitable in-line excess flow valve in UNLOADING LINES for non-refrigerated containers and pipe sizing does NOT restrict flow rates
Emergency shutoff OR backflow check valves in liquid AND vapor fixed piping of transfer system within 5 ft. or a reasonable distance from where hose/swivel piping is attached to fixed piping. Installed so that a break due to pull-away will occur on hose or swivel type piping side (NOT fixed piping side). This may be accomplished by using a bulkhead or equivalent anchorage, or by using breakaway/ shear fittings.
Emergency shutoff valve with MANUALLY ACTIVATED SHUTOFF FROM A REMOTE LOCATION and at the installed location.

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