Common Class 2 Hazardous Materials

The liquefaction of gases presents a hazard in itself. Liquefied gases have large liquid-to-gas expansion ratios. That is to say, a very small amount of a liquid leaking from a container can form a very large gas cloud. This increases the danger of flammability if an ignition source is present and asphyxiation or toxicity when vapor clouds form. Some liquefied gases such as propane and butane are ambient temperature liquids. Cryogenic liquefied gases, on the other hand, are very cold liquids. This difference in temperatures can cause problems for responders unless handled properly.

Liquefied Petroleum Gases—LF/HR

Liquefied petroleum gases (LPGs) include several similar mixtures that contain mostly propane and butane with small amounts of propylene and butylenes. A mixture does not change the chemical makeup of any of the components. Mixtures do, however, change the physical characteristics of the individual components to something between the highest and the lowest of the components physical characteristics. So the mixture has its own physical characteristics. Since propane is the primary LPG that is used in the United States, propane and LPG are often used synonymously.

Chemical Notebook Propane (C3HS) has a boiling point of -42°F and a vapor pressure of 858 at 21°C: kPa. Flammable range is 2.1-10.1 and its ignition temperature is 851°F. Propane expands from 1 gallon of the liquid to over 270 gallons of gas and is heavier than air (1.53). This means that a very small spill or leak can produce a large gas or vapor cloud. Both liquefied compressed and cryogenic gases can also produce a significant asphyxiation hazard in addition to any other hazards they might have. We are usually very aware of the flammability hazards of propane and other flammable gases, but we may overlook the asphyxiation hazard.

Liquefied gases are gases that have been liquefied by bringing the gas to its critical temperature and pressure. At this point, the gas turns into a liquid. Propane, for example, has a critical temperature of 206°F and a critical pressure of 617 psi. At that temperature and pressure, the propane gas becomes a liquid.

Butane (C4H10) has a boiling point of -0.4°F, a flammable range of 1.86-8.41, an ignition temperature of 761°F and an expansion ratio of 1 gallon of liquid to over 235 gallons of butane gas. It is heavier than air (2.00) and has a critical temperature of 306°F and a critical pressure of 555 psi. At that temperature and pressure, butane becomes a liquid.

Isobutane (t-C4H10) has a boiling point of -11.75°F, a flammable range of 1.80-8.44, an ignition temperature of 761°F and a vapor pressure of 215 at 21°C: kPa. Butane has an expansion ratio of 1 gallon of liquid to 234 gallons of gas, is heavier than air (2.07) and has a critical temperature of 134.6°C and a critical pressure of 3,650 kPa.

Propylene (C3FI6) has a flammable range of 2-11.1, an ignition temperature of 856, a boiling point of -53.9°F and a vapor pressure 146 at 0°C: kPa. It has a critical temperature of 197.5 and a critical pressure of 666.3.

Butylene (C4HS) has a flammable range of 1.98-9.65, an ignition temperature of 680, a boiling point of 21°F, a vapor density of 1.96 and a vapor pressure 1,939 at 21°C: kPa. It has a critical temperature of 40.2°F and a critical pressure of 146.4.

These gases are all hydrocarbons. You can see the differences in physical properties such as boiling points, ignition temperatures and vapor pressures based upon the compound. Flammable ranges are all similar because as a family the hydrocarbons have narrow flammable ranges. Vapor densities are also similar as most hydrocarbon gases except methane and ethane are lighter than air. Isobutane is branched in its structure. Branching has the effect of lowering the boiling point of the liquid, which allows it to be used in colder climates than butane.

Once liquefied, the gas is kept in the liquid state by pressurizing the tank to keep a constant artificial atmosphere pressing down on the liquid to prevent it from returning to the gas state. Liquids in these tanks are at atmospheric temperature. Irrespective of the temperature that is outside the tank, the liquid inside will be nearly the same. Liquefied gases exist in the tanks well above their boiling points. The only thing keeping the material from boiling and turning back to a gas is the pressure in the container.

These tanks are usually constructed of steel with working pressures generally between 100 and 500 psi. Propane has a working pressure of 250 psi, whereas anhydrous ammonia has a pressure of 265 psi. These tanks are never filled to the top. There is usually a 20% vapor space allowed above the liquid level. Usually, these tanks are not insulated but rather painted with white or aluminum paint to reflect radiant heat. When a pressure container such as the 331, with a boiling liquid inside, is exposed to flame on the vapor space, the container will quickly fail and produce a BLEVE, which is a boiling liquid expanding vapor explosion.

During a BLEVE, when the container opens up, all of the liquid inside instantly turns into a gas because it is existing above its boiling point. If there is an ignition source present, a fire ball may also be created. According to the National Fire Protection Association, BLEVEs occur within 8-30 min after flame impingement starts, with an average time of 15 min or less. If flame impingement occurs on the liquid level of the tank, the liquid in the tank will absorb the heat and protect the container. The heat from the fire will cause an increase in the pressure in the tank, and it will be vented through the relief valve.

If the relief valve cannot relieve the pressure as fast as it builds up, the container may still fail. Relief valves are only designed to relieve pressures created by increases in ambient temperature, not flame impingement. Excess flow valves are installed at product discharge openings. They operate in the event of a failure in discharge hoses or piping. Venting systems are either mechanical pressure relief or frangible disks. Valve protection during a rollover is much the same as that for other MC series tanks.

Class 2 Multiple Hazard Bad Actors Chemical Notebook

Chlorine (Cl2), LF/HR Because they are in such wide use, the hazards of common chemicals sometimes are taken for granted. Complacency can set in, and improper procedures may be used by those who work with the chemicals regularly and by emergency responders who deal with the materials during a release, resulting in injury and death. One of these chemicals is chlorine found in most communities in the United States as a gas or in compound with other chemicals that can release the chlorine when in contact with water or other chemicals. It is generally transported and stored as a liquefied compressed gas and is found in 100 to 150 lb cylinders, 1 ton containers and railroad cars.

Chlorine (elemental symbol: Cl) is a nonmetallic element, a member of the halogen family of elements with an atomic number of 17 on the periodic table. Other halogens include fluorine, bromine and iodine. Chlorine was discovered in 1774 by Carl Scheele, who also discovered oxygen and several other important compounds. Scheele called his discovery "dephlo- gisticated marine acid." Chlorine has an atomic weight of 35.453 and is a greenish-yellow diatomic gas with a pungent irritating odor, but it does not exist freely as a gas in nature. Diatomic gases are elements that do not exist as a single molecule, in this case Cl, but rather as the diatomic molecule Cl2. Other elements that are diatomic are hydrogen, nitrogen, bromine, iodine, fluorine and oxygen. (Oxygen is often referred to as 02 because it is a diatomic element.)

The primary source of chlorine is in the minerals halite (rock salt), sylvite and carnallite, and from the chloride ion (sodium chloride) in seawater. It can be liquefied for more economical shipping, storage and use.

Chlorine is toxic by inhalation (1 ppm in air), nonflammable, nonexplosive and a strong oxidizer (stronger than oxygen). Because chlorine is a strong oxidizer, it will support combustion even though it is nonflammable. Chlorine has a National Institute for Occupational Safety and Health (NIOSH) IDLH rating of 10 ppm and an exposure limit TWA of lppm. The Occupational Safety and Health Administration (OSHA) ceiling for chlorine is lppm. The maximum airborne concentration is 3ppm. This is the amount to which a person could be exposed for up to 1 h without experiencing or developing irreversible or other serious health effects or symptoms that could impair the ability to take protective action.

Chlorine gas irritates the mucus membranes, and the liquid burns the skin or causes irritation to the skin and may cause burning pain, inflammation and blisters. Tissue in contact with cryogenic liquid chlorine can cause frostbite injury. Chlorine's odor threshold is about 3.5 ppm, although some report that odor can be detected below the 1 ppm OSHA ceiling and TWA. Short-term exposure to low concentrations of chlorine (1-10 ppm) can result in sore throat, coughing and eye and skin irritation. After a few breaths at 1,000ppm, chlorine can be fatal. Exposures to chlorine should not exceed 0.5 ppm (an 8 h TWA over a 40 h week).

Chlorine is not known to cause cancer. Reproductive and developmental effects are not known or documented. It has a boiling point of 29°F, a freezing point of-150°F, a gas density of 2.5 (making it heavier than air), a specific gravity of 1.56 (heavier than water) and a vapor pressure of 5,168 mmHg at 68°F. The vapor pressure of chlorine is 53.1 psi at 32°F and 112.95 psi at 77°F.

Chlorine is slightly soluble in water and reacts with a variety of other chemicals, including aluminum, arsenic, gold, mercury, selenium, tellurium, tin and titanium. Carbon steel ignites near 483°F in contact with chlorine. It reacts with many organic materials creating violent or explosive results. Chlorine also reacts violently with acetylene, ether, turpentine, ammonia, fuel gas, hydrogen and finely divided materials. It is placarded and labeled as a Division 2.3 poison gas in transportation and OSHA-mandated fixed storage. Nonbulk containers will also have the corrosive label displayed. Chlorine has a UN four-digit identification number of 1017 and a National Fire Protection Association (NFPA) 704 designation of toxicity—3, flammability—0, reactivity—0 and special information oxy (oxidizer).

Chlorine was used during World War I as a choking (pulmonary) agent. One of the primary uses of chlorine around the world is in the chlorination of drinking water and treatment of sewage. It is also widely used in swimming pools. Chlorine is used in the production of paper products as a bleach and in dyestuffs, textiles, petroleum products, medicines, antiseptics, insecticides, food, solvents, paints, plastics and many other consumer products. Exposure to chlorine can cause various signs and symptoms depending on the amount and length of time exposed. There is no available antidote for chlorine exposure. Effects can be treated, and most people exposed that survive acute exposure will likely recover with little if any side effects. Listed below are potential symptoms:

  • • Coughing
  • • Chest tightness
  • • Burning sensation in the nose, throat and eyes
  • • Watery eyes (contact with liquid can cause blindness)
  • • Blurred vision
  • • Nausea and vomiting
  • • Burning pain, redness and blisters on the skin if exposed to gas and skin injury, similar to frostbite if exposed to liquid (cryogenic) chlorine
  • • Difficulty breathing or shortness of breath
  • • Fluid in the lungs

Exposure to low concentrations (1-10ppm) is likely to result in eye and nasal irritation, sore throat and coughing. Higher concentrations (greater than 15 ppm) are likely to result in rapid onset of respiratory distress with airway constriction and accumulation of fluid in the lungs (pulmonary edema). Additional symptoms may include rapid breathing, blue discoloration of the skin, wheezing, rales or hemoptysis. Pulmonary injury may progress over several hours and lung collapse can occur. It is estimated that the lowest lethal concentration for a 30 min exposure is 430 ppm. While these symptoms can also be present with exposure to other inhalation hazards, investigation of the site and circumstances should clear up the chemical involved in most cases.

Chlorine usually does not just appear; it has a distinctive color and odor. Examinations of containers and reports of witnesses can be helpful in positive identification. There are usually not any long-term health effects from sudden exposures to chlorine vapor for those who survive. Complications such as pneumonia during treatment can occur. Chronic bronchitis can also develop in people who contract pneumonia.

Although it is a gas, chlorine can cause irritation and burns in contact with the skin. Therefore, firefighter turnouts are not appropriate for chlorine exposures inside the "hot zone" of a hazardous materials incident. In the past, firefighters were known to wear firefighter turnouts with petroleum jelly covering the exposed skin. Chlorine is a poison gas and requires SCBA and full Level A chemical protective clothing for anyone knowingly going into an atmosphere where chlorine is present. OSHA allows Level В protection for unknown atmospheres, which could include chlorine, but as soon as it is known that chlorine is present, protection should be changed to Level A.

Generally, gases do not present a serious contamination concern, because it is unlikely they will stay on chemical protective clothing. When exposed to chlorine gas, responders will need to go through a minimal decontamination reduction corridor. Liquid exposure to chlorine or compounds of chlorine may require a more extensive decontamination effort. Victims will require decontamination quickly to reduce damage to skin and eyes. Emergency decontamination would be appropriate by first responders if done from a safe distance, avoiding vapor and runoff. Exposure of victims to gas will result in minimal contamination. Removing clothing can limit the exposure to liquid chlorine and any gas that may be trapped in the victims' clothing (Firehouse Magazine).

When released from a container, chlorine is most concentrated at the point of the release. As with many gases and vapors, the concentration diminishes the farther away from the source you get. Evacuation and isolation distances found in the DOT ERG are based on computer modeling of chlorine releases. Isolation (hot zone) for small spills (those from a small container or a small leak from a large container) is 100 ft. From a large container (several small containers or a large leak from a large container), the recommended isolation distance is 200 ft.

Evacuation distances are categorized into day and night spills. This is because the environment tends to be more stable at night, meaning a cloud will stay together longer and travel farther before dissipating. The evacuation distance for small day or night spills is one-tenth of a mile. The evacuation distance is three-tenths of a mile for a large day spill and seven- tenths of a mile for a large night spill. Several factors influence the amount of time a cloud of gas will stay together, including temperature, humidity, and wind direction and velocity. Chlorine dissipates best in warm, windy weather. It is a common industrial chemical in the top 10 produced chemicals annually. It is used and transported to and through almost any community in the United States, and releases do occur (DOT, ERG).

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