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DOT hazard classes

The department of transportation has developed a very good system for safely handling almost any chemical.  The developers have intelligently heeded the KISS concept: Keep It Simple Stupid.  Although, as Murphy says, it is impossible to make things fool proof, because fools are so clever.

To help people handle chemicals safely, they have been divided into nine categories.  Four of these categories are discussed later: Explosives, Compressed Gas, Radioactive, and ‘Other’.  The remaining classes are based on chemical properties that help us handle these chemicals safely.

1.  Class 3, Flammable liquids.  These types of chemicals have two important issues.  The first is that they cause/fuel fires, and the second is that they are volatile (like perfume).   The vapors from these chemicals can not only feed a fire, but they are often poisonous to breathe, or, they can displace all the oxygen in the air, leaving none to breathe.

Another issue for firefighters is that putting water on a gasoline fire only spreads the gasoline around, as well as the fire.  In Cleveland, the Cuyahoga River caught fire on June 22, 1969.  The river burned for thirty minutes, not the water, but the oil-like substances floating on top of the water.  For Firemen, spraying water on a river to put out a fire doesn’t work very well.

This is why there are different kinds of fire extinguishers, you can’t use water to put out all types of fires.  You should not use water to put out a grease fire in the kitchen, use the lid of a pot, sand (if available), or baking soda, otherwise you should have “dry chemical” type fire extinguisher.

Flammable liquids are often volatile, and if the cap is left off, or there is a hole if the container, the liquid will evaporate out and can become a breathing and fire issue.  Flammable liquids should be stored in a secure location that is isolated from living spaces, to ensure fumes don’t build up or get trapped inside to be breathed.  These vapors are flammable, and they can become an explosion hazard, similar to how fuel-air explosives work.

2.  Class 4 materials are reactive, sort of like nitroglycerine.  These chemicals can react with oxygen or water, and often need special handling procedures.  For example sodium metal must be kept in oil because it will react violently with water- even the water in the air.

There are also chemicals that react with water, like sodium hydrosulfite, which is a common rust remover (a reducing agent), and bleaching agent.  It is important for fireman to be aware of these compounds, because you don’t want to pour water on these materials during a fire as it will only make the emergency worse.

At one time miners used to use the chemical calcium carbide to generated a flame for their head lamps.  When this chemical is mixed with water it releases the gas acetylene (also used in acetylene torches), which ignites to produce light.  Obviously it would be very bad for a fireman to spray water on a fire when calcium carbide is involved.

3.  Class 5 materials are oxidizers, and they can release, and so provide, oxygen for a fire.  The increased oxygen makes the fire burn better, these materials help “fan the flames”.  The most dangerous of these provide oxygen, and fuel to a fire.  Some of the worst are organic peroxides, which often come (packaged separately) with epoxy resin, they act as a “hardener”.  These materials can not only be the fuel, but provide the oxygen and heat required for a fire to start.   Often car paint patching, or filling resins, come with a separate little tube of ‘hardener’.  These should be handled with care.

4.  Class 6 materials are poisons.  These chemicals generally come from deliberately created poisons like bug killer and weed killer.  There are instances where a poison only kills the pest of interest, but it is incorrect to think that a compound which poisons one species is ok for another, like DDT, poison is poison.  History (or hind-sight) shows us that what is safe (according to those who make it) one day, is toxic the next (after it kills people).

Inhalation Hazard Materials are included within this class, and refer to any volatile chemical which is poisonous like methylene chloride.  The designation ‘IDLH’: Immediately Dangerous to life or health, is used by DOT to indicate that a compound is volatile, and dangerous.  IDLH values were originally determined for 387 substances in the mid-1970’s, and IDLH values for 85 substances like benzene and methylene chloride, were determined by NIOSH to meet the OSHA definition of “potential occupational carcinogen” as given in 29 CFR 1990.103.  Unfortunately, many of these substances can be purchased down at the corner store, and at most require labeling of ORM-D (“Other Regulated Materials-Domestic”) for consumer commodities.

5.  Class 8 materials are corrosives- both acids and bases.  These are primarily cleaners.  For example, ‘Deck Cleaner’ can be either an acid, or a strong base.  The definition of corrosive is based on how fast that chemical will corrode some metal.  An interesting experiment is to put a nail in a glass of coke, and watch the nail corrode away over time;  This is due to the phosphoric acid in the ingredients.

The mob has/had a reputation for throwing acid in people’s face to blind or torture them.  The real story is that they actually used a strong base.  This is because acids are easily washed away, while bases dissolve tissue to generate soap.  Soaps are made by mixing a strong base with an oil, so a strong base turns your flesh into soap.  This is why strong bases feel ‘slimy’ and are hard to wash off because the soap created helps hold the strong base in place to dissolve more flesh.

The most notorious of these are the solid drain cleaners, like lye, or sodium hydroxide- probably the strongest base known.  The solid is ‘agroscopic’, meaning it absorbs moisture from the air, and that moisture becomes a very strong base.  It also generates a lot of heat when it dissolves in water, and a hot solution is more corrosive than a cold solution.  This is why people should not use the solid drain cleaners, especially with metal pipes.

The other Classes
Class 1 is Explosives, and these have obvious concerns.

Class 2 is the compressed gases, and they have the problem of explosively decompressing, plus, the gas itself  has properties, leading to additional class designations like flammable, corrosive, oxidizer, reactive, and sometimes radioactive.  Additionally, inert gases like helium or nitrogen can drive out, or displace, all of the oxygen in the air leading to suffocation issues- an air filter does not work if there is no ‘air’ to begin with.  This is why firefighters bring along their own compressed air tanks instead of using a filter. OSHA has a separate certification called ‘Confined Space Operation’, which deals with the issue of small spaces that may have had all of the oxygen driven out.  Many workers have been caught in, and suffocated in such a place.

Class 7 are Radioactive materials, and generally associated with the nuclear industry, and Medical ‘tracers’ and chemotherapy.

Class 9, or miscellaneous hazardous materials, or generally things like asbestos tiles, and CFLs(compact fluorescent Light bulbs), or fluorescent bulbs containing mercury.

The Next Section  is Routes of Exposure