Acetylene signs, their application and compliance

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What is Acetylene?

Acetylene is a colorless pungent-smelling hydrocarbon gas, which burns with a bright flame. Acetylene is used for welding and cutting. The welding process that uses acetylene is known as oxy-fuel cutting or gas cutting. Among all other gases, acetylene is capable of producing the hottest flame. For this reason, acetylene serves as an important medium for heat treating metals and other materials.

Fire Protection Guide to Hazardous Materials - Edition 14th

NFPA 49 Chapter 5 Hazardous Chemical Data Sheet

The Hazardous Chemical Data Compilation, previously known as NFPA 49, provides guidance on the hazards of chemicals to emergency personnel, safety professionals, inspection and enforcement officials on storage and fire fighting techniques that can be used in an emergency or in disaster planning.

Name: Acetylene, Dissolved

Formula: HC = CH

NFPA 30/OSHA Classification: n/a

DOT Class: Class 2.1, Flammable gas

Shipping Label: FLAMMABLE GAS

ID No: UN 1001

CAS No: 74-86-2

Statement of Hazards: Flammable Gas. Forms explosive mixtures with air over a very wide range. Low ignition energy. Reacts with active metals to form explosive compounds.

Emergency Response Personal Protective Equipment: Wear full protective clothing and positive pressure self-contained breathing apparatus.

Spill or Leak Procedures: Eliminate all ignition sources. Stop or control the leak if this can be done without undue risk. Use water spray to cool and disperse vapors and protect personnel.

Fire Fighting Procedures: Stop Flow of gas before extinguishing fire. Approach fire from upwind to avoid hazardous vapors and toxic decomposition products. Fight fire from protected location or maximum possible distance. Use water spray, dry chemical, foam, or carbon dioxide.

Health Hazards: Simple asphyxiant.

Fire and Explosion Hazards: Flammable gas. Forms explosive mixtures with air over a very wide range. Closed containers may rupture violently when heated.

Instability and Reactivity Hazards: Acetylene not dissolved in acetone may deflagrate above about 760 mm Hg absolute and becomes unstable at elevated pressures. It may decompose into hydrogen and carbon with explosive violence. Reacts with active metals (copper, silver, and mercury) to form explosive acetylide compounds. Reacts with chloride.

Storage Recommendations: Outside or detached storage is preferred. Isolate from oxidizing gases, especially chlorine. Store in a cool, dry, well-ventilated location. Store cylinders upright.

Physical Properties: Colorless gas with slight garlic-like odor..

Melting Point: -116°F (-82°C)

Boiling Point: -118°F (-83°C)

Solubility in Water: not soluble

Vapor Density: 0.9

Electrical Equipment: Cass I, Group A

Composition

Acetylene is a compound of the elements carbon and hydrogen. Its composition is expressed by the chemical symbol C2H2. On a weight basis, the proportion of the elements in acetylene is approximately 12 parts of carbon to 1 part of hydrogen, or 92.3% to 7.7%, respectively.

Physical and chemical properties

At atmospheric temperatures and pressures, acetylene is a colorless gas that is slightly lighter than air. Acetylene of 100% purity is odorless, but acetylene of ordinary commercial purity has a distinctive, garlic-like odor.

Acetylene burns in the air with an intensely hot, luminous, and smoky flame. The ignition temperatures of acetylene and mixtures of acetylene with air or acetylene with oxygen will vary according to composition, pressure, water vapor content, and initial temperature. As a typical example, mixtures containing 30% acetylene by volume with air at atmospheric pressure can be ignited at approximately 581°F (305°C). The flammable limits of mixtures of acetylene with air and acetylene with oxygen will depend on the initial pressure, temperature, and water vapor content. In air at atmospheric pressure, the upper limit of flammability is approximately 82% acetylene in air. The lower limit is 2.5% acetylene in air.

Acetylene can be liquefied and solidified with relative ease, but both liquid and solid acetylene are unstable. Mixtures of gaseous acetylene with air or oxygen in certain proportions can explode if ignited. Gaseous acetylene under pressure may also decompose with explosive force under certain conditions at low pressure, but experience indicates that 15 psig (103 kPa) is generally accepted as a safe pressure limit Generation, distribution through hose or pipe, or use of acetylene at pressures in excess of 15 psig (103 kPa) for welding and allied purposes is prohibited.

Pressure exceeding 15 psig (103 kPa) can be used with the use of special equipment. Where acetylene is used at pressures in excess of 15 psig (103 kPa) or transported through large diameter pipelines, means to prevent propagation if ignition occurs shall be used. Insulating large diameter pipes as a protection against exposure to fires is recommended. More specific information on low and medium pressure acetylene piping is included in CGA G-1.2, Acetylene Metering and Piping.

Acetylene cylinders prevent the decomposition characteristics of the gas by providing a porous mass packing material with minute cellular spaces so no pockets of appreciable size remain where "free" acetylene in gaseous form can collect. This porous mass is saturated with acetone or other suitable solvent in which the gaseous acetylene actually dissolves. The combination of these two features--the porous filler and solvent--allows acetylene to be contained in cylinders at moderate pressure without danger of explosive decomposition. Maximum cylinder pressure is 250 psig at 70 of (1720 kPa at 21.1 DC) with an approximate variation of 2.5 psi (18 kPa, differential) rise or fall in pressure for each degree Fahrenheit (0.56 DC) rise or fall in temperature.

Physical Constants of Acetylene

Physiological Effects

Commercial acetylene is generally considered a nontoxic gas that has been shown in experiments to have no chronic harmful effects even in high concentrations. In fact, it has been used as an anesthetic. Like most other gases, acetylene is a simple asphyxiant if present in such high concentrations that the lungs are deprived of their required supply of oxygen. In such cases, asphyxiation will result. It should be noted, however, that the lower flammable limit of acetylene in air will be reached well before asphyxiation can occur, and the danger of explosion is reached before any other health hazard is present.

Manufacture

Acetylene is usually manufactured by reacting calcium carbide and water to produce acetylene with calcium hydroxide [Ca(OH)₂] as a coproduct. For additional information refer to CGA G-1.5, Carbide Lime--Its Value and Uses. Acetylene may also be manufactured by the thermal or arc cracking of hydrocarbons or by a process using the partial combustion of methane with oxygen.

Acetylene manufactured from calcium carbide made in the United States and Canada normally contains less than 0.4% impurities other than water vapor. Apart from water, the chief impurity is air at concentrations of 0.2% to 0.4%. The remainder consists of trace quantities of phosphine, ammonia, hydrogen sulfide, and in some instances, small amounts of carbon dioxide, hydrogen, methane, carbon monoxide, organic sulfur compounds, silicon hydrides, and arsine. Purified cylinder acetylene is substantially free from phosphine, ammonia, hydrogen sulfide, organic sulfur compounds, and arsine. The other impurities are nearly the same as in the original gas.

Pipeline Use of Acetylene

Pipeline acetylene is used in the United States for chemical synthesis and for manufacturing carbon black. Acetylene is used in the manufacture of a variety of specialty chemicals and monomers that are used for organic synthesis, as solvents, and to make polymers used for plastics and synthetic rubber. The earlier uses for acetylene in the manufacture of commodity chemicals such as acetone, acetic acid, and acetaldehyde have been replaced by alternative raw materials.

Cylinder Use

The remaining acetylene production is principally used for oxy-acetylene welding, cutting, and heat treating.

Acetylene Cylinders

Acetylene is classified by the U.S. Department of Transportation (DOT) as a flammable compressed gas and it shall be shipped in steel cylinders manufactured to Specification DOT-8, DOT-8AL, ICC-8, ICC-8AL, DOT E-6517, DOT E-7542, or DOT E-10320 [10]. In Canada, acetylene is also classified by Transport Canada (TC) as a flammable compressed gas, and it shall be shipped in steel cylinders manufactured to Specification CTC-8, CTC-8AL, CTC-8WC, TC-8WM or TC-8WAM [10, 11].

Specifications DOT-8, DOT-8AL, ICC-8, ICC-8AL, DOT E-6517, DOT E-7542, and DOT E-10320 require that the steel used in cylinders meet certain chemical and physical requirements. These specifications also require that cylinder shells pass hydrostatic pressure tests, possess fillers of 92% or less porosity charged with a specified amount of solvent, and be protected by adequate pressure relief devices. Specifications and regulations governing the transportation of acetylene and other compressed gases are promulgated in the United States by DOT, which has federal authority for enforcement. In Canada, the requirements are specified in standards published by the Canadian Standards Association (CSA) and adopted into the Transportation of Dangerous Goods Regulations by TC [12].

Hazardous materials regulations of the DOT including specifications for shipping containers are published in Ti tle 49 of the U.S. Code of Federal Regulations (49 CFR) [10].

Acetylene in its free state under pressure can decompose violently with the evolution of heat. The decomposition can be initiated by shock, temperature, or reactive substances, and oxygen is not required either to initiate or sustain decomposition. The higher the pressure, the smaller the initial energy input required to cause decomposition. To minimize the hazards of storing and transporting acetylene, it can only be compressed into specially constructed DOT and TC approved cylinders packed with a porous, inert absorptive solid material that is saturated with a solvent. Cylinders used with all other compressed gases are unsuitable for charging with acetylene, and other gases shall not be charged into acetylene cylinders. Acetylene mixed with any other gas shall not be charged into an acetylene cylinder.

Acetylene is generally available in cylinders having capacities from 10 ft ³ to 420 ft³ (0.3 m³ to 11.9 m³).

Filling Limits

Because of the characteristic of any gas or liquid confined in a closed container to increase in pressure with rising temperature, the possibility always exists that a cylinder charged with gas at a safe pressure at normal temperatures would reach a dangerously high pressure at high temperatures. To prevent this from happening during normal use, DOT and TC have regulations that limit the amount of solvent and acetylene that may be charged into a cylinder. These regulations provide that the internal pressure of a cylinder when filled may not exceed 250 psig (1720 kPa) at 70 °F (21.1 °C).

Marking and Labeling

The following marks are required by DOT or TC to be plainly stamped on or near the shoulder or top head of all acetylene cylinders:

— cylinder specification (example: DOT-8, DOT-8AL, ICC-8, ICC-8AL, DOT E-6517, DOT E-7542, DOT E-10320, CTC-8, CTC-8AL, CTC-8WC, TC-8WM or TC-8WAM);

— serial number and the manufacturer's identifying symbol, which shall be registered with DOT or TC;

— date the cylinder was tested by the manufacturer;

—tare weight

The tare weight of the acetylene cylinder consists of the combined weights of the following:

— cylinder shell;

— porous mass;

— fusible metal pressure relief device;

—solvent

—saturation gas;

—valve

If at any time the valve is removed for replacement, extreme care shall be taken to ensure that the new valve has the identical weight so the tare weight stamped on the cylinder remains correct. If the new valve weight is heavier or lighter by 1 oz (28.4 g) on cylinders of 75 ft³ (2.1 m³) capacity or less, or by 2 oz (56.8 g) on cylinders of more than 75 ft³ (2.1 m) capacity, then the tare weight stamped on the cylinder shall be changed to reflect the new weight. This change can only be made in accordance with DOT or TC requirements.

The required markings on cylinders shall not be changed except as provided by DOT or TC regulations. Markings on cylinders shall be kept in a legible condition.

Acetylene cylinders shall be legibly marked with the proper shipping name and identification number:

ACETYLENE

UN1001

Such Markings:

— shall be made by means of stenciling, stamping, or labeling;

— shall not be readily removable; and

— shall be in accordance with CGA C-7, Guide to Preparation of Precautionary Labeling and Marking of Compressed Gas Containers.

DOT regulations require that in addition to marking of the proper shipping name and identification number on a cylinder, a 100 mm (3.9-in) diamond (square-on-point) red label (designating a flammable gas) having the number 2 in the lower corner be attached to each cylinder containing acetylene when offered for transportation. This includes rail, common, contract, or private motor carriers.

Alternately, DOT regulations allow the use of 30 mm (1.25-in) square-on-point labels as long as the cylinder(s) are not overpacked and are durably and legibly marked in accordance with CGA C-7, Appendix A. See 49 CFR 172.400a.

In Canada, the general requirement is for each side of a label to be at least 100 mm in length with a line running 5 mm inside the edge. However, if that size label, together with the shipping name, technical name, and UN number, cannot be displayed because of the irregular shape or size of the small means of containment, each side of the label may be reduced in length by the same amount to the point where the label, together with the shipping name, technical name, and UN number, will fit that small means of containment, but must not be reduced to less than 30 mm. In Canada, hazard class wording is not allowed on labels; whereas, in the United States, it is optional.

Refiling

United States and Canadian regulations forbid the shipment of cylinders containing acetylene unless they were charged by or with the consent of the owner. In addition, cylinders may be charged only by a person or company having possession of complete information on the nature of the porous filler, the kind and quantity of the solvent in the cylinders, and the meaning of the markings on the cylinders.

Storing Acetylene Cylindes at User's Premises

When storing acetylene cylinders, the user shall comply with all local, state, federal, provincial, and municipal regulations, and with the standards of the National Fire Protection Association (NFPA) and the International Code Council (ICC). See NFPA 51, the I-Codes, and 29 CFR Part 1910.253 [2,16,17]. In addition, the user should also consult and follow the practices described in CGA P-1, Safe Handling of Compressed Gases in Containers.

Rules for Storing Acetylene

The following are rules for storing acetylene cylinders:

— For the sake of safety and orderliness, cylinders should always be stored in an assigned location bearing in mind that acetylene is a flammable gas stored under pressure.

— Acetylene cylinders should be stored in a dry and well-ventilated location.

—Because of the rapid rise of pressure in the cylinder with increasing temperature, cylinders shall not be stored at temperatures exceeding 125 °F (51.7 °C) and shall not be used at temperatures above 120 °F (48.9 °C). Acetylene cylinders should not be stored near sources of heat such as radiators and furnaces, or potential sources of heat such as highly combustible materials like gasoline, oil, waste, etc.

— Acetylene cylinders should not be stored near elevators, gangways, or in locations where heavy moving objects may strike or fall against them. Dropping a cylinder or subjecting it to abnormal mechanical shock is likely to damage the cylinder, valve, or fusible metal pressure relief device.

— Acetylene cylinders should not be stored in close proximity to oxygen cylinders. Unless separated by a minimum distance of 20 ft (6.1 m), a noncombustible partition 5 ft (1.5 m) high having a fire-resistive rating of at least 1 hr. should be between stored acetylene cylinders and oxygen cylinder.

NOTE — Single cylinders of acetylene and oxygen may be stored secured on a cart or used adjacent to each other without a partition. Additionally, single cylinders of acetylene and oxygen located at a work station (e.g. chained to a wall or building column or secured on a cart) shall be considered "in service".

— Acetylene cylinders stored inside a building shall be limited to a total capacity of 2500 ft³ (70.8 m³ ) of acetylene exclusive of cylinders in use or attached for use. Quantities exceeding this total shall be stored in a special building or in a separate room as required by NFPA 51 [2]. In buildings and rooms housing acetylene operations, ventilation shall be provided and no open flames for heating or lighting shall be permitted.

— Storage should be planned so cylinders are used in the order in which they are received from the supplier.

— Valve protection caps, when provided for in the cylinder design, shall be mechanically attached except when cylinders are in actual use.

— Conspicuous signs should be posted in the storage area forbidding smoking or the carrying of open flame.

— Empty cylinders should be stored separately from full cylinders. Empty cylinders should be marked with the letters MT or EMPTY to avoid confusion.

— Valves shall be closed on all cylinders when not in use and when the cylinders are empty.

— Cylinders should be stored and used in a vertical position. Use in a secured vertical position enhances safety by providing for easy access to the valve and regulator assembly.

— When storing acetylene cylinders outdoors, they should be protected from the ground to prevent bottom corrosion. During the winter, cylinders stored in the open should be protected against accumulations of ice or snow. In summer, charged cylinders stored in the open should be screened against the direct rays of the sun in those localities where extreme temperatures prevail.

— Stored cylinders should be protected from individuals without authorized access.

— Do not store acetylene cylinders, particularly small cylinders used for soldering, in confined spaces such as drawers, closets, unventilated cabinets, automobile trunks, or toolboxes. Acetylene cylinders should not be stored or transported in automobiles or any enclosed vehicle.