Document ID: PHMSA-2007-0061-0002
Agency: phmsa
Document Type: Notice
Title: Safety Advisory Guidance: Use of Mobile Acetylene Trailers
Posted Date: 2007-09-06T04:00Z

[Federal Register: September 6, 2007 (Volume 72, Number 172)]
[Notices]               
[Page 51297-51301]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr06se07-125]                         

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DEPARTMENT OF TRANSPORTATION

Pipeline and Hazardous Materials Safety Administration

[Docket No. PHMSA-2007-29133; Notice No. 07-08]

 
Safety Advisory Guidance: Use of Mobile Acetylene Trailers

AGENCY: Pipeline and Hazardous Materials Safety Administration (PHMSA).

ACTION: Safety advisory notice; request for comments.

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SUMMARY: This safety advisory is addressed to persons involved in the 
use, operation, fabrication, or other handling of mobile acetylene 
trailers. In this notice, we discuss recent acetylene incidents, 
requirements in the Hazardous Materials Regulations, national consensus 
standards issued by the Compressed Gas Association and National Fire 
Protection Association, operating procedures, fire mitigation and 
detection systems, and training of persons who operate, charge, and 
discharge mobile acetylene trailer systems. We urge companies and 
workers to review their operating practices to ensure that filling and 
discharge operations are conducted in the safest possible manner. In 
addition, we are requesting information on the effectiveness of current 
DOT regulations and industry best practices, as well as suggestions for 
enhancing the safety of these operations.

DATES: Submit comments by November 5, 2007.

ADDRESSES: You may submit comments identified by the docket number 
(PHMSA-2007-29133) by any of the following methods:
     Federal eRulemaking Portal: http://www.regulations.gov. 

Follow the instructions for submitting comments.
     Web Site: http://dms.dot.gov. Follow the instructions for 

submitting comments on the DOT electronic docket site.
     Fax: 1 202 493 2251.
     Mail: Docket Operations, U.S. Department of 
Transportation, West Building, Ground Floor, Room W12-140, Routing 
Symbol M-30, 1200 New Jersey Avenue, SE., Washington, DC 20590.
     Hand Delivery: Docket Operations, U.S. Department of 
Transportation, West Building, Ground Floor, Room W12-140, Routing 
Symbol M-30, 1200 New Jersey Avenue, SE., Washington, DC 20590 between 
9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    Instructions: You must include the agency name and docket number 
(PHMSA-2007-29133) for this notice at the beginning of your comment. 
Internet users may access comments received by the Department of 
Transportation at http://dms.dot.gov Note that comments received may be posted without change to http://dms.dot.gov. including any personal 

information provided.

FOR FURTHER INFORMATION CONTACT: Ben Supko, Office of Hazardous 
Materials Standards, Pipeline and Hazardous Materials Safety 
Administration, (202) 366-8553, or Charles Hochman, Director, Office of 
Hazardous Materials Technology, Pipeline and Hazardous Materials Safety 
Administration, (202) 355-4545.

SUPPLEMENTARY INFORMATION:

I. Background

    Acetylene is a highly flammable gas that requires special packaging 
and handling procedures to be transported safely. Acetylene is 
regulated as a Division 2.1 flammable gas under the Hazardous Materials 
Regulations (HMR;

[[Page 51298]]

49 CFR parts 171-180) and is subject to stringent packaging and 
handling requirements. Acetylene is filled and transported in cylinders 
containing a porous mass and solvent; transportation in bulk containers 
is prohibited.
    In place of bulk packaging, mobile acetylene trailers (MATs) are 
used to transport large quantities of acetylene. The Compressed Gas 
Association (CGA) defines a MAT as a group of cylinders, secured 
together as a unit, mounted on an open transport vehicle, and 
manifolded for containing and transporting acetylene.
    On July 25, 2007, shortly after 9 am, at a Southwest Industrial 
Gases facility in Dallas, Texas, a MAT delivered by Western 
International Gas and Cylinders Inc. caught fire while the trailer was 
being prepared to discharge acetylene to the facility. The origin of 
the fire has not been identified. Witness reports state that a small 
fire began at the rear of the trailer and then spread to cylinders in 
the facility. The fire burned for more than an hour and ruptured a 
number of cylinders with explosive effects. Three people were injured. 
The fire caused the closure of local streets and Interstates 30 and 35E 
for much of the day and destroyed four trailers at the Southwest 
Industrial Gases facility. Both the Chemical Safety Board (CSB) and 
National Transportation Safety Board (NTSB) are investigating the 
incident; PHMSA is assisting with the investigations.
    On August 7, 2007, just north of Houston, Texas, outside of the 
Hughes Christensen Co., a fire started on a MAT delivered by Western 
International Gas and Cylinders, Inc. None of the cylinders ruptured, 
and firefighters were able to douse the acetylene cylinders with water 
and keep the fire confined to the trailer. No one was hurt, but 800 
employees were evacuated. NTSB and CSB are also investigating this 
incident; PHMSA is participating in the investigations.

II. PHMSA Regulations

    The HMR specify requirements for the safe transportation of 
hazardous materials in commerce by rail car, aircraft, vessel, and 
motor vehicle. The hazardous material regulatory system is a risk 
management system that is prevention-oriented and focused on 
identifying a safety or security hazard and reducing the probability of 
and consequence from a hazardous material release. Under the HMR, 
hazardous materials are categorized into hazard classes and packing 
groups based upon the risks they present during transportation. The HMR 
specify appropriate packaging and handling requirements for hazardous 
materials, and require a shipper to communicate the material's hazards 
through use of shipping papers, package marking and labeling, and 
vehicle placarding. The HMR also require shippers to provide emergency 
response information applicable to the specific hazard or hazards of 
the material being transported. Finally, the HMR mandate training 
requirements for persons who prepare hazardous materials for shipment 
or who transport hazardous materials in commerce. The HMR also include 
operational requirements applicable to each mode of transportation. The 
HMR apply to each person who offers a hazardous material for 
transportation in commerce, causes a hazardous material to be 
transported in commerce, or transports a hazardous material in commerce 
(see 49 CFR 171.1(b) and (c)).
    Under the HMR, acetylene is regulated as a Division 2.1 flammable 
gas. Acetylene is only authorized for transportation in DOT 
specification 8 or 8AL cylinders or in UN cylinders conforming to ISO 
3807-2 (see 49 CFR 173.303). Transportation of acetylene in bulk 
packagings, such as cargo tanks, portable tanks, or rail tank cars is 
prohibited. Section 173.301(f) requires cylinders to be equipped with 
one or more pressure relief devices sized and selected as to type, 
location, and quantity, and tested in accordance with CGA S-1.1 and S-
7. For acetylene, CGA S-1.1 requires DOT 8 or 8AL cylinders to be 
fitted with a CG-3 fusible plug, which operates at 212[deg]F. The plug 
must be proven using the fire test method specified in CGA publication 
C-12. To ensure the stability of the acetylene during transportation, 
cylinders are constructed with porous filler and are charged with 
solvent. The porous filler is typically calcium silicate, and the 
solvent is typically acetone or dimethylformamide. The amount of 
solvent and porous filler must be closely monitored to prevent 
overfilling. Sections 178.59(l)(4)(i) and 178.60(p)(4)(i) establish 
requirements regarding the amount and porosity of the porous filler and 
maximum amount of solvent authorized based on the water capacity of DOT 
8 and 8AL cylinders.
    The HMR permit acetylene cylinders to be manifolded during 
transportation (see 49 CFR 173.301(g)(1)(iii)). However, the manifolded 
cylinders must conform to the following conditions: (1) Manifolded 
branch lines must be sufficiently flexible to prevent damage to the 
valves; (2) the cylinders must be supported and held together as a unit 
by structurally adequate means; (3) each cylinder must be equipped with 
an individual shutoff valve that is tightly closed in transit and an 
individual pressure relief device that discharges upward; and (4) the 
valves and pressure relief devices must be protected from damage by 
framing, a cabinet, or other method.
    The requirements for the transportation of hazardous materials by 
highway are found in Part 177 of the HMR, including requirements for 
loading and unloading hazardous materials from highway transport 
vehicles. When cylinders containing acetylene and other Class 2 gases 
are transported in commerce, they must be securely restrained in a 
manner that prevents shifting, overturning, or ejection from the motor 
vehicle under normal transportation conditions (see 49 CFR 
177.840(a)(1)). Normal transportation conditions include vehicle 
starting, stopping, cornering, accident avoidance, and varied road 
conditions. We request comments pertaining to the adequacy of current 
securement requirements for cylinders, including whether existing 
securement measures would withstand the force of an accident or 
rollover. Comments should consider the protection from damage afforded 
to manifolded cylinders by framing, cabinets, or other methods, as 
required by Sec.  173.301(g)(1)(iii)).
    Except for cargo tanks and portable tanks, the HMR generally 
prohibit the discharge or emptying of a package's contents prior to its 
removal from the motor vehicle (see 49 CFR 177.834(h)). However, this 
general prohibition does not apply in all circumstances. For example, 
it has been our longstanding interpretation that the prohibition in 
Sec.  177.834(h) does not apply to tube trailers, which are 3AX, 3AAX, 
and 3T cylinders mounted to a transport vehicle, because removing them 
from the motor vehicle prior to discharging their contents is not 
practicable. We have long applied the same standard to discharge 
operations involving manifolded acetylene cylinders that are mounted to 
a transport vehicle.

III. National Consensus Standards

    Several national consensus standards apply to the generation, 
storage, movement, and use of acetylene. The standards cover filling 
and discharge operations for acetylene cylinders and the transportation 
of such cylinders. Persons involved in these operations should 
thoroughly review these standards to ensure that they are utilizing 
appropriate safety practices. Below we list and summarize applicable 
national consensus standards.

[[Page 51299]]

A. CGA G-1, Acetylene

    This standard, developed by the Compressed Gas Association (CGA), 
provides general information on the characteristics of acetylene and 
proper handling procedures. The publication begins by describing the 
manufacturing process, composition, properties, and the physiological 
effects of acetylene. It continues by detailing the HMR requirements 
that apply to shipments of acetylene. It describes authorized 
packaging, valves, pressure relief devices, filling limits, and hazard 
communication. In addition, it outlines safe methods for storing 
acetylene cylinders at a fixed facility location and safe methods for 
handling and using acetylene. The standard concludes by discussing the 
type of piping that is suitable for acetylene.

B. NFPA 51A--Standard for Acetylene Cylinder Charging Plants

    This standard, published by the National Fire Protection 
Association (NFPA), establishes safeguards for the design, 
construction, and installation of acetylene cylinder charging plants. 
The standard applies to plants that are engaged in the generation and 
compression of acetylene and charging of cylinders with acetylene. The 
standard applies to the location, arrangement, construction, design, 
and development of facilities used in the generation of acetylene and 
also includes valuable information regarding the charging of manifolded 
cylinders. In fact, Chapter 10 of the NFPA 51A standard specifically 
addresses facility-based acetylene cylinder charging manifolds. Though 
the standard does not provide specific transportation-related 
information, the safety precautions recommended for facility-based 
charging stations are very similar to those used to charge MATs, 
including:
     Charging manifolds must have a shutoff and blowdown valve 
vented outside or to the low pressure system.
     A check valve must be installed in the facility pipeline 
at each cylinder charging manifold and lead.
     Pressure gauges must be protected by a device that stops a 
detonation of flame and limits a rise in pressure.
     Manifold outlets must have a shutoff valve.
     Manifolds must be arranged to limit stress in the cylinder 
charging leads.
     In order to prevent liquefying of acetylene at low ambient 
temperatures, specific maximum charging pressures based on ambient air 
temperature must be followed.
     Cylinder valves must be opened first at the start of 
charging and closed last at the end of charging.
     Acetylene cylinders connected to charging manifolds must 
have provisions for cooling by water spray applied from a manually 
activated spray nozzle system where needed for removing heat from 
solution acetylene, as determined by ambient temperature and cylinder 
charging rate.

C. CGA G-1.6, Recommended Practices for Mobile Acetylene Trailer 
Systems

    In this publication, CGA provides safe practices for the design, 
construction, and operation of MATs. The publication also provides 
recommended safe practices for auxiliary equipment used in conjunction 
with MATs, including piping, regulators, flash arrestors, and meters. 
The standard specifically addresses the following areas:
    1. Design and construction (CGA G-1.6, Section 4)
     Trailer must conform to all applicable Federal, state, and 
local regulations.
     A grounding system for the piping that conforms to NFPA 
70, National Electrical Code, must be provided to ground the piping 
system.
     Piping must: be carbon steel, stainless steel, wrought 
iron, malleable iron, or copper alloys containing not more than 65% 
copper; conform to the American National Standard Institute A13.1, 
Scheme for Identification of Piping Systems; be braced and supported; 
and meet the appropriate Schedule based on pressure.
     Leads between cylinders and manifolds must be sufficiently 
long and flexible to minimize strain on valves and leads.
     Manifolds must be equipped with a shut-off valve, pressure 
gauge, and vent.
     Vents and pressure relief devices must be directed upwards 
above the acetylene piping.
     Protective equipment must be installed between a MAT and 
facility piping.
     Cylinders must: conform to the HMR; be vertical, 
supported, and secured; have valves that are capable of being closed in 
the event of an emergency; have similar functional characteristics, 
including dimensions, porous mass, solvent, and solvent quantity; and 
be arranged in aisles to allow access.
    2. Operation (CGA G-1.6 Section 5)
     To be charged, cylinders must conform to applicable HMR 
requirements.
     Cylinders must be marked in accordance with CGA C-7, 
``Guide to the Preparation of Precautionary Labeling and Marking of 
Compressed Gas Containers.''
     In order to prevent liquefying of acetylene, specific 
maximum charging pressures based on ambient air temperature must be 
followed.
     During cylinder charging, valves are to be opened first 
and closed after the pressure between manifolded cylinders equalizes 
(takes several hours).
     Valves must be closed during transportation.
     Acetylene pressure must be maintained in leads and 
manifolds during delivery and return shipments.
     Legible instructions must be posted at the discharge 
location when consumers use any equipment to discharge the acetylene.
     The trailer must be chocked or secured to prevent movement 
during discharge.
     During any manual valve operations, or when the trailer is 
being connected or disconnected, a trained person must be in 
attendance.
     When acetylene is discharged in an enclosure, appropriate 
venting to the outside must be used.
     The flow rate of acetylene for intermittent withdrawal 
from the trailer must not exceed 10% of the trailer capacity per hour, 
for continuous withdrawal the flow rate should not exceed 6.6% (1/15) 
of the trailer capacity per hour.
    3. Associated equipment (CGA G-1.6, Section 6)
     The trailer discharge station must be in conformance with 
NFPA 50, ``Standard for Bulk Oxygen Systems at Consumer Sites'' and be 
a minimum distance of 50 feet from property lines, bulk flammable 
liquid storage, and non-acetylene bulk flammable gas storage.
     The trailer must be a minimum distance of 25 feet from 
property lines, 50 feet from combustible construction, and 15 feet from 
non-combustible construction.
     The trailer site must: Provide adequate space for 
positioning the trailer and be protected with curbing or guardrails; be 
not exposed to power, flammable liquid, flammable gas, or oxidizing 
lines; be equipped with signage stating ``ACETYLENE--FLAMMABLE GAS'NO 
SMOKING--NO OPEN FLAMES'; and have a grounding system for the trailer.
     Appropriate hoses, meters and electrical equipment must be 
used.
    4. General provisions (CGA G-1.6, Section 7)
     MATs must be marked and placarded in accordance the Part 
172, Subparts D and F of the HMR.
     Charging and discharging stations for MATSs must be 
provided with

[[Page 51300]]

conspicuously located and easily accessible fire hoses or fixed spray 
systems and dry chemical fire extinguishers. Nozzles on fire hoses 
should be of the type that adjusts from full stream to a fog pattern.
     Exits and fire protection equipment may not be blocked or 
obstructed.

IV. Recommended Practices

    The standards summarized above outline specific procedures for 
filling, discharging, and transporting acetylene cylinders and for 
storing and using acetylene. Based on our review of the recent 
incidents and the applicable national consensus standards, we recommend 
that entities involved in the transportation of acetylene, particularly 
the filling and discharge of manifolded cylinders mounted on a motor 
vehicle, implement safety procedures conforming to applicable sections 
of CGA G-1, ``Acetylene (1990), NFPA 51A Standard for Acetylene 
Charging Plants'' (2006 Edition), and CGA G-1.6, ``Recommended 
Practices for Mobile Acetylene Trailer Systems,'' (1996, Fourth 
Edition, Reaffirmed 2001). In addition, entities must ensure that 
acetylene cylinders fully comply with all HMR requirements applicable 
to the specification cylinder, including cylinder components such as 
valves, pressure relief devices, porous filler, and solvent.
    The CSB Web site provides several examples of best practices to 
mitigate fires, including the use of fire monitors and water deluge and 
sprinkler systems. We strongly recommend that entities involved in the 
transportation of acetylene review the best practices highlighted by 
CSB and implement those that apply to their operations. In particular, 
facility operators should consider the installation of fire monitors 
and water deluge or sprinkler systems. In the event of a cylinder fire, 
the presence of such fire mitigation systems will help cool the 
cylinders, reducing the likelihood of additional gas releases, cylinder 
ruptures, and other potentially catastrophic consequences. For 
additional information, the CSB's Web site provides best practices 
based on a Praxair Flammable Gas Cylinder Fire that occurred in St. 
Louis, MO on June 24, 2005. A safety bulletin and video addressing the 
Praxair incident can be found at http://www.csb.gov/index.cfm?folder=completed_investigations&page=info&INV_ID=59#
.

    The acetylene accidents covered in this safety advisory notice 
occurred in conjunction with our assessment of the safety risks 
associated with bulk loading and unloading operations. On June 14, 
2007, we hosted a public workshop to examine industry data, identify 
industry best practices and standards, discuss the role of recommended 
practices, and consider industry actions that have the potential to 
reduce risk during loading and unloading. Representatives from 
industry, federal agencies, state and local government, standards 
organizations, the emergency response community, employee groups, 
environmental and public interest organizations, and the public 
participated in the meeting. As a result of this collaborative effort 
between PHMSA and our stakeholders, we developed a set of recommended 
practices that are generally applicable to loading and unloading 
operations involving hazardous materials in many different types of 
packagings and a number of different operational and modal contexts. 
Consistent with these recommended practices, we recommend that shippers 
and carriers of acetylene develop and implement specific procedures for 
loading and unloading operations that are based on an assessment of the 
safety risks associated with the type of loading or unloading operation 
being conducted and the material or materials involved. Please consider 
the following guidelines when developing operating procedures for 
acetylene:
    (1) Make sure employees know and understand their specific 
responsibilities during loading and unloading operations, including 
attendance or monitoring responsibilities.
    (2) Identify and implement appropriate safety precautions, 
including measures specific to the material transported, such as 
pressure or temperature controls and maximum filling limits; necessary 
protective equipment; controlling access to the area where the 
operations take place; procedures for connecting and disconnecting 
piping, hoses, and connections; ignition sources; and procedures for 
monitoring the loading and unloading operations.
    (3) Identify and implement appropriate pre-transfer procedures, 
including pre-transfer inspections of the transport unit, packaging, 
transfer area, and piping, hoses, or other connections are free of 
defects, leaks, or other problems that could result in an unsafe 
condition.
    (4) Identify and implement appropriate transfer procedures;
    (5) Identify and implement appropriate emergency procedures, 
including identification of emergency response equipment and 
individuals authorized in its use; incident response; use of emergency 
shut-down systems; and emergency communication and spill reporting.
    In addition, we remind entities that offer for transportation or 
transport acetylene cylinders that their employees must be trained. In 
accordance with the requirements in Subpart H of Part 172 of the HMR, 
persons who directly affect hazardous materials transportation safety 
must complete training that covers the following:
    1. General awareness training designed to familiarize each employee 
with the requirements of the HMR and to enable each employee to 
recognize and identify hazardous materials.
    2. Function-specific training designed to ensure that each employee 
understands how he is to perform the functions or operations for which 
he is responsible. Training for employees responsible for loading or 
unloading operations should include training on established procedures 
applicable to such operations, as well as national consensus standards 
that have been incorporated into such procedures.
    3. Safety training concerning emergency response information 
applicable to the specific hazardous material(s) handled, measures to 
protect the employee from the hazards associated with the materials to 
which the employee may be exposed in the work place, and methods and 
procedures for avoiding incidents.
    4. Security training that provides an awareness of the security 
risks associated with hazardous materials transportation and methods to 
enhance transportation security.
    We believe that the procedures outlined above, including those 
contained in the CGA and NFPA standards, combined with a rigorous 
training program, will ensure that persons responsible for filling, 
operating, and discharging MATs have the knowledge and information to 
enable them to conduct these operations safely. We urge shippers and 
carriers engaged in these operations to evaluate their current 
operations, review the national consensus standards, and make 
adjustments in procedures and practices where necessary to minimize the 
safety risks associated with the transportation of acetylene on MATs.

VI. Enhanced Safety Program for Mobile Acetylene Trailers

    We plan to work with acetylene shippers and carriers, emergency 
responders, associations such as CGA and NFPA, government agencies 
concerned with the safe handling and use of acetylene, and other 
stakeholders to assess the effectiveness of current

[[Page 51301]]

safety procedures used for filling, operating, and discharging MATs to 
determine whether additional safety procedures should be implemented. 
To this end, we request that persons who use such transportation 
systems to provide us with information on the effectiveness of the 
current DOT regulations, consensus standards, and industry best 
practices. We are also interested in any other procedures utilized to 
ensure that operations related to the transportation of acetylene on 
MATs are performed safely.
    We would also like to work with shippers, carriers, and facilities 
that receive shipments of acetylene in MATs to develop and implement a 
pilot program to test the effectiveness of current or alternative 
procedures or methods designed to enhance the safety of transportation 
operations involving acetylene on MATs. As part of this program, we 
will assist individual companies or facilities to evaluate the 
effectiveness of their current procedures and to identify additional 
measures that should be implemented. We welcome suggestions concerning 
how such a program should be structured and the entities that should 
participate.
    To ensure that our message reaches all stakeholders affected by 
these risks, we plan to communicate this advisory through our public 
affairs notification and outreach processes. For additional visibility, 
we have made this advisory available on the PHMSA homepage at http://www.phmsa.dot.gov and the DOT electronic docket site at http://

dms.dot.gov. In addition, if you are aware of other companies that are 
involved in the charging, operating, and discharging MATs, please share 
this advisory notice with them and, if possible, identify them in your 
correspondence with this agency. We believe a collaborative effort 
involving an integrated and cooperative approach will help us to 
address safety risks, reduce incidents, enhance safety, and protect the 
public.

    Issued in Washington, DC on August 30, 2007.
Theodore L. Willke,
Associate Administrator for Hazardous Materials Safety.
[FR Doc. 07-4355 Filed 9-5-07; 8:45 am]

BILLING CODE 4910-60-P