Thursday

Scuba Cylinders and Title 49 of the Code of Federal Regulations

Here are the hard and fast regulations that we must follow as gas blenders and safe divers.
 
No cylinders will be overfilled more than 10% period.
Here are the facts.


FICTION: Fill Station Operators do not have to be trained
FACT:  The truth is that the US Code of Federal Regulations, Title 49, requires "Function Specific" training for all employees.  If they fill cylinders they need Fill Station Operator training.
In Canada the rules are even more specific.  Transport Canada regulation CSA-B340 requires that persons filling containers be trained although it does not specify the exact nature of that training.
FICTION: The Code of Federal Regulations is not law.
FACT:  While technically true, 44 USC 1507 (public law) requires that the Federal Register be “judicially noticed”, that is, recognized by the courts as law.  All aspects of the CFR have been first printed in the Federal Register and the CFR is prima facie evidence of the text of the original documents as published in the Federal Register. 
In short, while the CFR may technically be regulation and not law, you will never win that argument in court.
FICTION:       Compressed air is not a designated Hazardous Material.
FACT:  Compressed air is a HAZMAT.  49CFR173.115 defines a compressed air at 40.6 psia or greater at 68ºF as a Class 2, Division 2.2 HAZMAT.
FICTION:       Formal training in HAZMAT is not required.
FACT:  Absolutely wrong!  49CFR172.702 requires a hazmat employer to ensure that each of its hazmat employees is provided appropriate function specific training and to ensure that each of its hazmat employees is tested by appropriate means. 49CFR172.704 goes on to specify what this training must consist of.  This training must be completed within 90 days of employment or change in job function and then every three years thereafter.
FICTION:       Persons who receive no compensation but who handle high pressure cylinders are not required to have formal and documented HAZMAT training.
FACT: This is one of the most onerous myths of all. 49CFR171.8 defines a HAZMAT employee as one who, among other things, is employed by a hazmat employer and who in the course of employment directly affects hazardous materials transportation safety. This term includes an individual, including a self-employed individual, employed by a hazmat employer who, during the course of employment loads, unloads, or handles hazardous materials.
Do not confuse “employed” with “paid”.  Employ means to use, whether there is compensation involved or not. Those divers who just hang around a dive store asking to help and who are used by the dive store to move, load and fill cylinders require formal and documented function specific training just as much as do paid employees.  Not conducting this training can be very costly.
Furthermore. § 1910.101   Compressed gases (general requirements) provides for: (a) Inspection of compressed gas cylinders. Each employer shall determine that compressed gas cylinders under his control are in a safe condition to the extent that this can be determined by visual inspection. Visual and other inspections shall be conducted as prescribed in the Hazardous Materials Regulations of the Department of Transportation (49CFR parts 71–179 and 14CFR103). Where those regulations are not applicable, visual and other inspections shall be conducted in accordance with Compressed Gas Association Pamphlets C–6, C-6.2, C-6.2 and C6.3 which are incorporated by reference as specified in §1910.6.
FICTION:     The inspection guidelines of Compressed Gas Association (CGA) Pamphlets C-6, C-6.1, C-6.2, and C-6.3 are not mandatory.
FACT: 49CFR180.205 incorporates these publications “by reference” into the CFR itself.  As such, the guidance on these publications are to be considered by US courts as being part of the Code of Federal Regulations and treated as if they were Federal Law.
 CGA C-6 is entitled Standards for Visual Inspection of Steel Compressed Gas Cylinders
CGA C 6.1 is entitled Standards for Visual Inspection of High Pressure Aluminum Compressed Gas Cylinders
CGA C-6.2 is entitled Guidelines for Visual Inspection and Requalification of Fiber Reinforced High Pressure Cylinders
CGA 6.3 is entitled Guidelines for Visual Inspection and Requalification of Low Pressure Aluminum Compressed Gas Cylinders
FICTION:     A steel cylinder may not be authorized for a 10% excess fill after the first hydrostatic retest.
FACT:    The US Code of Federal Regulations establishes the requirements for pressurizing steel cylinders beyond their stamped service pressure.  49CFR173.302 sets forth the requirements for pressurizing cylinders 10% in excess of its marked service pressure.  These requirements are:
1)     Cylinder must be 3A or 3AA (steel)
2)     Cylinder must be equipped with the proper frangible (burst) disc.
3)     Cylinder’s must have been tested or retested using the hydrostatic water jacket method
4)     Neither the average nor maximum wall stresses exceed the limits established in the CFR
5)     An external and internal visual inspection made at the time of the test or retest shows the cylinder to be free of excessive corrosion, pitting or dangerous defects.
6)    A plus sign “+” is added following the test date marking.
 The use of the term “test or retest” clearly authorizes hydrostatic retest facilities to reauthorize an appropriate cylinder for a 10% excess fill.  Is this common?  No.  Is it legal?  Yes.
FICTION:       Steel cylinders do not have to be visually inspected for cracks.
FACT:  Yes they do.  CGA Pub. C-6 lists a crack inspection as part of the inspection procedure – and remember that C-6 has been “incorporated by reference” into the CFR.
FICTION:       A condemned cylinder must be rendered incapable of holding air by drilling a hole in the sidewall or by destroying the neck threads.
FACT:  49CFR180.207 prescribes the procedures for the condemnation of cylinders.  They are to be condemned by stamping a series of “X”s over the DOT specification number and the service pressure or by stamping “CONDEMNED” on the cylinder shoulder. Only at the direction of the cylinder owner may the requalifier render the cylinder incapable of holding pressure.  Additionally, the cylinder owner must be notified IN WRITING that the cylinder is condemned and may not be filled with a hazardous material.
 Cylinders failing hydrostatic retest or visual inspection cannot be returned to their owner without being condemned.  However, those facilities that destroy your cylinder neck threads or drill a hole in the sidewall WITHOUT YOUR PERMISSION are in violation of the law.
FICTION:       The law requires all 6351-T6 alloy aluminum cylinders to be inspected with an eddy current tester.
FACT:  49CFR180.205 requires only that 6351 alloy cylinders in SCUBA, SCBA and oxygen service be eddy current tested at time of hydrostatic requalification.
FICTION:       6351-T6 alloy aluminum is still authorized for the manufacture of high pressure 3AL cylinders.
FACT: 49CFR178.46 is the specification for 3AL seamless aluminum cylinders.  It specifies 6061-T6 alloy only. 
 This DOES NOT mean that existing 6351-T6 alloy cylinders are to be pulled from service.  It only means that no new 3AL cylinders can be manufactured from this alloy.
FICTION:       All 6351-T6 alloy cylinders have been recalled.
FACT: This is closely related to the above myth and is absolutely untrue.   49CFR178.46 simply no longer authorizes 6351-T6-T6 for future manufacture on 3AL cylinders (all new 3AL cylinders must be manufactured using 6061-T6 alloy).  6351-T6 cylinders in use may be used so long as they remain within established hydrostatic testing and visual inspection standards for continued service.   Postulating this myth to customers is unethical.
 FICTION:       No special training is required to visually inspect the Luxfer fiber wrapped (FRP2) SCUBA cylinder E12479
FACT: DOT Special Permit SP-12479 specifically requires that the cylinder be given an annual visual inspection by a Professional Scuba Inspectors, Inc. (PSI) certified person.
FICTION:       An external visual inspection of a cylinder is not required before filling
FACT: 49CFR173.301 requires that before each cylinder filling the person filling it must visually inspect the outside of the cylinder for cracks, leaks, bulges, defective valve, leaking or defective burst disc, evidence of physical abuse, fire or heat damage, and detrimental corrosion.  Any such cylinder may not be filled.
 Failure of the Fill Station Operator (FSO) to conduct this routine informal visual inspection may have a highly memorable consequence.
FICTION:       Paintball and Spare Air cylinders do not require hydrostatic retesting
FACT:  Even though paintball and Spare Air cylinders are filled by the cylinder owner, they still require periodic requalification.  49CFR180.205 requires that each cylinder bearing a DOT specification marking be requalified (hydrostatically retested) as specified in the Requalification Table of section 180 of the CFR. Cylinders bearing a DOT Special Permit number (SPxxxxx) must be requalified in conformance the terms of the applicable Special Permit.
 There is an exception.  49CFR180.209 Table 1 exempts cylinders not exceeding 2 inches outside diameter AND less than 2 feet in length from periodic volumetric expansion tests.  If either dimension exceeds the limit a periodic requalification is required.   Paintball cylinders and most Spare Air cylinders usually exceed at least one of these limits. 
FICTION:       Steel cylinders with a marked service pressure of 2400 psig are low pressure cylinders
FACT:  Nothing could be further from the truth.  CGA Pub C-6 defines a high pressure steel cylinder as one containing pressures of 900 psig or greater – and don’t forget that CGA Pub C-6 has been “incorporated by reference” into the CFR.
 Strangely, the high pressure definition for aluminum cylinders is different. CGA C-6.1 defines a high pressure aluminum cylinder as one containing pressures of 1800 psig or greater.
FICTION:       Aluminum cylinders manufactured prior to 1990 are no good.
FACT:       To tell a customer this boders on fraud.  The only place where the US DOT has established a terminal use date for cylinders are in the various  Special Permits for the fiber wrapped cylinders.  The terminal date for wrapped cylinders is usually 15 years, but some Carbon Fiber wrapped cylinders are now authorized a 30 year life.  3A, 3AA and 3AL cylinders, even 6351 alloy aluminum cylinders,  are authorized for continued service as long as they are within established hydrostatic test and visual inspection standards.
FICTION:       Cylinders are hydrostatically tested to 5/3 of their stamped Service Pressure
FACT:  While this is generally true, cylinders containing a stamped test Pressure (TP) are to be tested to the specified test pressure.  Usually, but not always, this is 3/2 service pressure rather than 5/3.
FICTION:       A cylinder exposed to excessive heat must be condemned.
FACT: While simple exposure to high heat may require a cylinder to be pulled from service for further examination, it does not condemn a cylinder.  Condemnation requires some portion of the cylinder itself to be heated to the specified temperature.
 49CFR 180.203 defines overheating as a condition in which the temperature of any portion of an aluminum cylinder has reached 176 °C (350 °F) or higher, or in which the temperature of any portion of a steel or nickel cylinder has reached 343 °C (650 °F) or higher.  The various Special Permits governing fiber wrapped cylinders specify overheating as when any portion of the aluminum liner reached a temperature of 250 ºF.
FICTION:       The Code of Federal Regulations does not apply to me because I am not in interstate commerce
FACT:  In establishing the applicability of the CFR, 49CFR171.1 uses the term “in commerce” which has been misinterpreted by many as meaning in commercial and interstate commerce.  If we read the CFR further, however, we find in 49CFR171.8 that it defines “commerce” more broadly as meaning “trade or transportation in the jurisdiction of the United States within a single state; between a place in a state and a place outside of the state; or that affects trade or transportation between a place in a state and place outside of the state” (Emphasis mine).
 Do you use state and federal roads and highways to transport your Division 2.2 Hazmat (compressed air) to/from a dive site or an emergency?  If so, the code applies to you.
FICTION:       The Exemption or Special Permit number on a cylinder is the authorization to manufacture cylinders and has nothing to do with the longevity of the cylinder.
FACT:  In order for an E or SP cylinder to remain in service its Special Permit (as of 1 Jan 2006 the terminology has again changed and Exemptions are again called Special Permits) must be current.  That means it must be in effect.  Requalifiers are required by DOT to have on hand the "current" Special Permit of the cylinder being requalified.  If the Special Permit has expired it cannot be current.  Hence the cylinder is no longer authorized for service.
FICTION:       DOT/TC cylinders, when in need of a requalification, may be requalified by either a DOT or a TC authorized requalifier and then be filled and transported in both the United States and Canada.
FACT:  While a cylinder manufactured to DOT/TC standards may be used and transported in both Canada and the United States, when the cylinder receives its periodic hydrostatic test requalification its usability may be limited.  To be filed and transported in the United States it MUST be requalified by a USDOT authorized requalifier.  To be filled and transported in Canada it MUST be requalified by a TC authorized requalifier.
FICTION:       There is no authority for SCUBA cylinders to have an annual visual inspection.  This is just a standard of practice in the SCUBA industry
FACT:  In CGA Pub P-5 Paragraph 6.1 the Compressed Gas Association requires all cylinders in SCUBA service to be visually inspected annually.
FICTION:       All UN cylinders may be used to transport hazardous material in the United States
FACT:  To be transport hazardous material in the United States UN cylinders must bear the additional marking of USA or CAN (alternatively, US or CA).
FICTION:       All Aluminum cylinders manufactured prior to 1990 must be eddy current tested.
FACT:  Using the date 1990 is the lazy and inaccurate method of determining cylinder alloy. 
49CFR180.209 requires only cylinders manufactured of 6351 alloy to be eddy current tested.  Not all cylinders manufactured prior to 1990 meet this criterion.  NO Catalina cylinder is made from this alloy regardless of its date of manufacture.  ALL Walter Kidde cylinders were made from this alloy.  Only SOME Luxfer cylinders were made from this alloy.  For SCUBA. SCBA and Oxygen  cylinders Luxfer phased a changeover in alloys from 6351 to 6061 over an thirteen month period from May 1987 through June 1988 and based it on cylinder size.
To ascertain the specific alloy for Luxfer cylinders you need to refer to the Luxfer Technical Bulletin dated November 12, 2003.  Here is a link to the Luxfer document.
FICTION:       The usability of the PSI Evidence of Inspection sticker expires.
FACT:  Unlike other EOI stickers which show the year of the visual as the last two digits in the century (00-99), the PSI-PCI sticker shows the year of the inspection as the last single digit in the decade (0-9).  Determining the decade of the inspection is really not significantly more difficult than determining the century of the inspection. If there is confusion as to the decade, a simple look at the hydro date should help. You NEVER have to replace your sticker inventory because you passed the highest two digit date on the sticker. 
Part 173 - Shippers - General Requirements for Shipments and Packaging
Subpart A-General
173.1 Purpose and Scope
173.1(a)(1)(2)(3)
 This part includes: Definitions of hazardous materials for transportation purposes; requirements to be observed in preparing hazardous materials for shipment by air, highway, rail, or water; and inspection, testing and retesting responsibilities for persons who retest, recondition, or maintain compressed gas cylinders used in the transportation of hazardous materials.
173.2 Hazardous materials classes and index to hazard class definitions.
Relative to scuba cylinders, the Class No. of the hazardous materials being considered is a"2", the Division No. is "2.2" and the name of the class or division is non-flammable compressed gas", and the 49CFR reference for definitions is 173.115
173.6 Materials of trade exceptions
When transported by a motor vehicle in conformance with this section, a material of trade (see 171.8) is not subject to any other requirements... besides those set forth or referenced in this section. (Section 6 of part 173)
173.6(a) Materials and amounts A material of trade is limited to...:
173.6(a)(2) A division... 2.2 material in a cylinder with a gross weight not over... 220 pounds
173.6(b) Packaging
173.6(b)(1) Packaging must be leak tight... and securely closed, secured against movement, and protected against damage
173.6(b)(5) A cylinder...containing Division 2.2 material must conform to packaging, qualification, maintenance and use requirements of this subchapter (subchapter C).  Manifolding of cylinders is authorized provided all valves are tightly closed.
173.6(c) Hazard Communication
173.6(c)(3) a DOT specification cylinder... must be marked as prescribed in this subchapter.
173.6(c)(4) The operator of a motor vehicle that contains a material of trade must be informed of the presence of the hazardous material... and must be informed of he requirements of this section. (173.6)173.6(d) Aggregate gross weight
...the aggregate gross weight of all materials of trade on a motor vehicle may not exceed 440 pounds.
Subpart B - Preparation of Hazardous Materials for transportation
173.23 Previously authorized packaging
173.23(a) 
When regulations specify a packaging with specification marking prefix "DOT", a packaging marked prior to January 1, 1970, with the prefix "ICC" may be used in it's place if the packaging otherwise conforms to applicable specification requirements. The markings on older scuba cylinders contain the prefixed ICC, the markings on newer scuba cylinders contain the prefix DOT
173.23(c) After July 2, 1982, a seamless aluminum cylinder manufactured in conformance with and for use under DOT special permit (SP) or exemption (E) 6498, 7042, 8107, 8364 or 8422 may be continued in use if marked before or at the time of the next retest with either the specification identification "3AL" immediately above the special permit or exemption number, or the DOT mark... in proximity to the special permit or exemption marking.
173.34 Qualification, maintenance and use of cylinders
173.34(a) General qualification for use of cylinders
173.34(a)(1) No person may charge or fill a cylinder unless it is specified in this part (Part 173) and part 178 (All American made and/or marketed Scuba Cylinders meet this requirement) A cylinder that leaks, is bulged, has defective valves or safety devices, bears evidence of physical abuse, fire or heat damage, or detrimental rusting or corrosion, must not be used unless it is properly repaired and re-qualified as prescribed in these regulations.
173.34(b) Grandfather clause. A cylinder in domestic use previous to the date upon which the specification therefore was made effective in these regulations may be used if the cylinder has been properly tested and otherwise complies with the requirements applicable for the gas with which it is charged. Currently here are few, if any "grandfathered" cylinders being used as scuba cylinders. However, any such cylinders which continue to pass their hydrostatic retests and their five year and annual visual inspections and continue o be suitable for the gases intended to be contained may be continued to be used.
173.34(c)Cylinder Marking. Each required marking on a cylinder must be maintained so that it is legible. Retest markings and original markings which are becoming illegible may be reproduced by stamping on a metal plate which must be secured to the cylinder.
173.34(c)(1) Additional information not affecting the markings prescribed in the applicable cylinder specification may be placed on he cylinder (applies o such information as annual evidence of inspection stickers, allowing them to be placed)
173.34(c)(3) Markings required on cylinders may not be altered or removed the exception to this is that the marked service pressure may be changed but only after a lengthy and involved procedure not typically pursued by recreational scuba divers (and not allowed for cylinder which have failed their periodic hydrostatic retesting unless reheat treated and requalified in accordance with this section [frankly speaking, not something to be pursued])
173.34(d) Pressure relief device systems. Cylinders must be equipped with one of more pressure relief devices per CGA Pamphlet S-1.1
173.34(d)(1) Safety devices are not required on cylinders 12 inches in length or less (exclusive of neck) and 4.5 inches or less in outside diameter. A pressure relief device is required on a cylinder charged with nonliquified gas to a pressure of 1800psi or higher a 70 degrees F (Scuba cylinders fall into this category)
173.34(e) Periodic qualification and marking of cylinders.
173.34(e)(1)(2) Every 5 years cylinders with the following specification marks (3A, 3AA or 3AL) must be retested to 5/3 times he service pressure, or to the test pressure marked on the cylinders shoulder when such is present. (what his means is that a cylinder's markings need o be carefully scrutinized prior to the retest procedure to determine  to what pressure he cylinder is to be retested. No cylinder maybe charged (filled) unless that cylinder has been inspected and retested and the retester has marked the cylinder appropriately. The retest must be performed by an authorized retester (A person holding a current retester's identification number issued by the Associate Administrator for Hazardous Material Safety.
173.34(e)(3) Visual Inspection.. each time a scuba cylinder is retested, it must be visually inspected, internally and eternally, in accordance with CGA Pamphlets C-6, C-6.1 as applicable.
The only requirement in the Code of Federal Regulations for visual internal and external examination is at the time of retest (once every 5 years, etc) Annual visual inspections are by mutual agreement... scuba cylinder owners submit their cylinders for annual inspections to individuals known to have been trained and certified to do annual inspections.
A person who only performs visual inspections on DOT or ICC specification cylinders is not required to obtain a retester identification number. However, a compressed gas cylinder may only be rejected by a person who has obtained such a retester identification number
173.34(e)(4) Pressure retest. Each cylinder required to be retested must be retested by means suitable for measuring the expansion of the cylinder under pressure (interior hydrostatic pressure in a water jacket, or other suitable apparatus)
173.34(e)(5) Cylinder rejection
173.34(e)(5)(i) A retester shall reject a cylinder when on visual inspection, it meets rejection standards in CGA pamphlet C-6, C-6.1 as applicable
173.34(e)(5)(iii) When a cylinder is rejected, the retester shall notify the cylinder owner in writing that the cylinder has been rejected and may not be filled.
In general, scuba cylinders which have been rejected should be condemned. A cylinder can only be rejected by an approved tester.
173.34(e)(6) Cylinder condemnation.
A scuba cylinder must be condemned when: upon inspection, it meets a condition of condemnation in CGA Pamphlet C-6 or C-6.1 (as appropriate); the cylinder leaks through its wall; there is evidence of cracking the extent that the cylinder is likely to be weakened appreciable; or permanent expansion exceeds 10% of total expansion. A cylinder is condemned by having a series of X's stamped over the ICC or DOT specification number and the marked service pressure.. or the word CONDEMNED is stamped on the shoulder.. or.. a the direction of the owner he cylinder is rendered incapable of holding pressure. When a cylinder is required to be condemned, the retester shall notify the cylinder owner, in writing that the cylinder is condemned and may not be filled. A cylinder can only be condemned by an approved retester. Steel scuba cylinders condemned because of excessive permanent expansion may reheat-treated (see note above) 3AL cylinders (aluminum) condemned because of excessive permanent expansion may not be reheat-treated.
173.34(e)(7) Retester Markings
Each cylinder passing retest must be marked with the cylinder retester's identification number set in a square pattern, between the month and year of retest date. The retester's identification number must be in characters not less than 1/8 inch high. Dates of previous tests must not be obliterated.
173.34(e)(8) Recordkeeping
The Code of Federal Regulations only identifies retesters (persons holding current retester identification numbers from the associate administrator for Hazardous Material Safety) as individuals who shall maintain records (current retester identification number issuance letters, daily records of visual inspections, hydrostatic retests, etc)
173.34.(e)(16) DOT-3A or 3AA cylinders. Defines so-called "star service". "Star service does not apply to cylinders used for diving, but may apply to cylinders in dive store compressed gas banks. A cylinder made in compliance with specification DOT-3A or DOT-3AA not exceeding 125 pounds water capacity (Steel scuba cylinders meet this criterion) and removed from any cluster, bank, group, rack or vehicle each time it is filled may be retested every 10 years instead of every 5 years provided the cylinder complies with all of the following:
  • Was manufactured after December 31, 1945
  • Used exclusively for air or certain other gases (argon, helium, nitrogen, oxygen or permitted mixtures)
  • Passes the CGA Pamphlet C-6 hammer test prior to each refill
  • Is stamped with a five-pointed star following the test date
  • Is dried inside immediately following hydrostatic testing
  • The cylinder is not used for underwater breathing
Some hydro-station and air fill station personnel misinterpret the "Star Service" description to mean that certain steel cylinders ("old") ones must be taken out of service. They are mistaken.
173.34(f) Cylinders subjected to the action of fire. Such cylinders must not again be placed in service until they have been properly reconditioned. Aluminum scuba cylinders subjected to the action of fire shall not be reheat treated and must be removed from service. Certain steel cylinders subjected to the action of fire shall be hydrostatically retested, other steel cylinders shall be reheat treated and reconditioned as specified in paragraph G.
173.34(g) Reheat treatment. The description is lengthy, and the process is involved. It will be safer and simpler to condemn such a cylinder (one which was subject to the action of fire) and remove it from service.
173.34(h) repair by welding or brazing of specification DOT-3A, DOT-3AA, ...cylinders.. describes a lengthy procedure not applicable to steel scuba cylinders and not at all applicable to aluminum ones. Frankly speaking, any scuba cylinder deemed to require repairs by welding or brazing should instead be condemned and removed from service.
Subpart C - Definitions, Classification and Packaging
Class 1
173.50 Class 1 - Definitions
173.50(a) 
An explosion is defined as an extremely rapid release of gas and heat. When a scuba cylinder under pressure ruptures, there is no release of heat. Although such incident can not technically defined as "explosions" they will always be described as such
Subpart D - Definitions, Classification, Packing Group Assignments and Exceptions for (certain) Hazardous Materials
173.115 Class 2 Division 2.2 - Definitions
173.115(b) 
Division 2.2 (Non-flammable, non-poisonous compressed gas-including compressed gas and oxidizing gas) For the purpose of this subchapter, a non-flammable, non-poisonous compressed gas (Division 2.2) means any mixture which-
173.115(b)(1) exerts in the packaging an absolute pressure of 40.6psia or greater at 68 degrees f. The gases in scuba cylinders referenced in this book meet this definition
173.115(d) Non Liquefied compressed gas. A non-liquefied compressed gas mean a gas, other than in a solution, which in a packaging under the charged pressure is entirely gaseous at a temeperature of 68 degrees f. The gases in scuba cylinders referenced in this book meet this definition
173.115(i) Service Pressure. The expression service pressure means the authorized pressure marking on the packaging. For example, for a cylinder marked "DOT3A1800", the service pressure is 1800psi
Subpart G - Gases; Preparation and Packaging
173.300a Approval of independent inspection agency
173.300a(a) 
Any person who does not manufacture cylinders.. and... is not directly or indirectly controlled by any person or firm which manufactures cylinders... may apply to the Department of Transportation for approval as an independent inspection agency for the purpose of performing cylinder inspections and verifications... require by part 178 (A very involved process)
173.301 General Requirements for shipment of compressed gases in cylinders...
173.301(b) Ownership of a container. A container charged with a compressed gas must not be shipped unless it was charged by or with the consent of the owner of the cylinder
173.301(c) Retest of Container. A container for which prescribed periodic retesting has become due must not be charged and shipped until such retest has been properly made.
173.301(d)(1) Manifolding containers in transportation. Manifolding of compressed gas cylinders is allowed for containers of argon, air, helium, nitrogen (or) oxygen, provided that each container is equipped with a pressure relief device [per 173.34(d)]
173.301(e) Container Pressure. The pressure in the container at 70 degrees f must not exceed the service pressure for which the container is marked or designated except as provided in 173.302(c) [173.302(c) describes the "10% overfill" allowed for some steel cylinders
173.301(f) Container pressure a 130 degrees f. The pressure in he container at 130 degrees f shall not exceed 5/4 times the service pressure.
173.301(h) Compressed gas containers. Compressed gases must be in metal containers built in accordance with DOT specifications in effect at time of manufacture.
173.301(i) Foreign cylinders in domestic use. Foreign cylinders are allowed in the USA provided they were manufactured, inspected and tested in accordance with the applicable DOT specification set forth in part 178
173.301(j) Charging of foreign cylinders. If the foreign cylinder is not manufactured, inspected and tested in accordance with DOT/ICC specifications it can only be charged for export.
173.302 Charging of cylinders with non-liquefied compressed gases.
173.302(a) 
Detailed requirements. Cylinders of compressed gases must be shipped, per 173.301 and 173.305 in the following containers:
173.302(a)(1) Specification 3A and 3AA (to mention only two). Applies to cylinders of compressed air, cylinders of compressed oxygen, cylinders of compressed helium, cylinders of compressed nitrogen and cylinders of compressed argon.
173.302(a)(5) Authorizes the use of aluminum cylinders (DOT 3AL) for compressed air, argon, helium, nitrogen and oxygen (to mention only a few)
173.302(a)(5)(i) In oxygen service, 3AL aluminum cylinders must be equipped only with brass or stainless steel valves
173.302(a)(5)(ii) In oxygen service, aluminum cylinders (DOT3AL) must be equipped only with straight threads in the neck opening.
173.302(a)(5)(iii)(iv) In oxygen service, aluminum cylinders (3AL) must be cleaned in compliance with the requirements of Fed Spec R-C-901b (Aug 7, 1967), paragraphs 3.7.2and 3.8.2 Cleaning agents equivalent to those specified in RR-C-901b may be used provided they are not capable of reacting with oxygen. One cylinder selected at random from a group of 200 or less, cleaned at the same time, must be tested for oil contamination in accordance with RR-C-901b paragraph 4..4.2.3 and meet the standard of cleanliness specified, and when used in oxygen service, the pressure in the aluminum cylinder may not exceed 3000psig at 70 degrees f
173.302(b) Filling limits. The pressure in the container at 70 degrees f must not exceed the service pressure for which the container is marked or designated. The only exception to this filing limit is provided in 173.302(c) which follows below.. and which does not apply to 3AL aluminum cylinders. 3AL aluminum scuba cylinders must not be overfilled.
173.302(c) Special filling limits for specifications 3AA cylinders. This is the regulation which permits 10% over-fill of certain steel cylinders. Steel cylinders may be over-filled by 10%, provided:
  1. Such cylinders are equipped with frangible disc safety relief devices (without fusible metal backing) having a burst pressure not exceeding the minimum prescribed test pressure
  2. Such cylinders were last tested or retested by the water jacket method
  3. for DOT 3AA cylinders the average wall stress shall not exceed 67,000PSI or the maximum wall stress shall not exceed 73,000 psi maximum. These figures in no way represent the pressure of gas in the cylinder, This wall stress is the internally (within the steel itself) distributed  force-per-unit-area mechanical reaction of the steel resulting from he deformation (stretching of the steel)
  4. An external and visual examination made at the time of test or retest shows the cylinder to be free from excessive corrosion, pitting or dangerous defects.
  5. That a plus sign (+) be added following the test date marking on the cylinder to indicate compliance with (c)(2), (c)(3) and (c)(4) above.
173.305 Charging of cylinders with a mixture of compressed gas and other material. Applies to nitrox, trimix etc
173.305(a)
 Detailed requirements. If the mixture is a compressed gas, that mixture must be treated as a compressed gas in accordance with these regulations
173.306 Limited Quantities of compressed gases
173.306(a) Limited quantities of compressed gases (air, argon, helium, nitrogen and oxygen, to name a few) are excepted from labeling (except when offered for transportation by air). In addition, shipments are not subject to subpart F of 172 (placarding), nor to part 174 (Carriage by rail) except 174.24, nor to part 177 (Carriage by public highway) except 177.817. Each package may not weigh more than 66 pounds gross weight