The Chemistry behind Hazcatting
Hazcat’s Cyanide Test
comparisons to Cyanide Tests from other systems
Hazcat vs 5-Step – Comparisons
Testing for Cyanides:
– The 5-Step Kit only prompts the user to check for a cyanide compound when the pH of the unknown is 10-14. The Hazcat Kit prompts you to look for the cyanide anion in solids and liquids with a pH of 3-14
There are several common cyanide salts that are either insoluble in water and/or have a neutral pH. Many of these cyanide salts are still reactive with acids and are still very hazardous. These hazards are not found by the 5-Step system.
These cyanide salts include copper cyanide (pH 7), mercuric cyanide (pH 8), silver cyanide (pH 8), zinc cyanide (pH 7)…
– The Hazcat Kit will look for the cyanide anion in samples that test positive in the Oxidizer Test. The 5-Step Kit states in it’s manual: “Samples that give a positive oxidizer test cannot contain cyanides.” This is not true. Certain oxidizers such as sodium hypochlorite and hydrogen peroxide will convert cyanides to cyanates which removes the “cyanide” hazard”, but there are many more oxidizers on the list of compounds that give a positive oxidizer test that do not have that effect on cyanides. Also, there are compounds such as copper cyanide, that all by itself gives a positive Oxidizer Test. Chromium cyanide also gives a positive Oxidizer Test due to the transition metal.
Cyanide salts can also be mixed with several types of oxidizers without being oxidized to a cyanate. As such a sample could be positive oxidizer and still contain cyanides.
Compounds that give a positive Oxidizer Test, that can be mixed with a cyanide salt without any noticeable reaction, and whose mixture still gives a positive Oxidizer Test include:
• Sodium Percarbonate
• Potassium Chlorate
• Potassium Chromate
• Copper Sulfate
– The Hazcat Kit’s Cyanide Test 1 has no interferences, no false positives, no false negatives. The 5-Step Kit’s Cyanide Test has interferences that give false positives and false negatives:
False Positive: Thiocyanates – sodium thiocyanate, potassium thiocyanate, mercury thiocyanate
False Negative: When a cyanide is mixed with a: bromide, iodide, chromate, permanganate, or a strong reducing agent such as: tin chloride, sodium sulfite, sodium borohydride or zinc metal, a false negative may occur.
More False Negatives: Copper cyanide, palladium cyanide, mercuric cyanide and silver cyanide can give a false negative.
– The Hazcat Kit’s Cyanide Test 1 will work in any matrix. If the cyanide compound is mixed with a paint or a dye, the test still works, because it looks for hydrogen cyanide gas in the atmosphere above the unknown. The 5-Step Kit relies on a color reaction (the appearance of a violet color) occurring on a strip of test paper that is immersed into the unknown. If the matrix is strongly colored or a paint then this can interfere with the ability to read a color change on the test strip.
– The Hazcat Kit’s Cyanide Test 1 requires only 1ml of a liquid unknown sample or ½ spoonful of a solid unknown sample.
– The 5-Step Kit requires 5ml of a liquid unknown sample and does not give instructions on how to test an unknown solid.
– The reagents used in Hazcat’s Cyanide Test 1 do not have a shelf life. The 5-Step Kit’s Cyanide Test has a 2½ year shelf life.
Oxidizers, KI Paper, Hydrobromic Acid
Haztech’s Oxidizer Test is employed in the system to identify more than just oxidizers. The path towards identification of many transition metal salts employs a “positive” oxidizer test paper result that could be considered a “false positive” outside of the hazcat system. Concentrated sulfuric acid can be identified by the exothermic dehydration of the paper itself leading to portions of the paper being charred away. Phosphorous pentoxide in solid form gives the same reaction of charring the paper. Other color changes can occur on the paper: Certain mercury salts, bismuth nitrate and hydriodic acid are indicated when the paper takes on a yellow or orange color. Sodium borohydride is indicated by a tan, gold color. Certain lithium salts are indicated by a pink coloration.
When Oxidizer Test paper is used within the HazCat System there are specific procedures that are required such that the observations gained during it’s use send the enduser down the right path. These procedures should only be employed when the oxidizer paper is used within the hazcat system (i.e., when the enduser is following hazcat’s flow chart and test instructions to identify a material). Hazcat copyrighted the test procedure that involved adding 3N HCl to the paper back in the early 80’s, and the procedure was never meant to be used outside of the hazcat flowchart. Many field ID screening systems used by START contractors, clean-up companies, Hazard Classification Systems that are marketed for sale copied hazcat’s procedure and incorporated it into the group of tests they use to screen substances. A positive result on the paper outside of using it in the manner prescribed in the hazcat system does not necessarily mean that the substance is an oxidizer. One good example of a substance that is not an oxidizer that does give a strong positive response is benzoquinone – which is actually a toxic, flammable solid – not an oxidizer.
The paper manufacturer’s state that the KI paper doesn’t need HCl to work and that is true…. But without it many of the Oxidizers that the HazCat System does key out with it would not give a positive response. The addition of HCl helps ionize many of the inorganic reactive oxidizers and brings them into solution so that the paper can soak up the oxyanions quickly and more uniformly. Using the paper dry, without HCl can also give false positives when the unknown is a liquid. Solutions of substances such as ferric chloride and copper sulfate will give a positive response on dry (no HCl) KI paper.
Without the HCl many crystalline oxidizing substances would give a very spotty reaction on the paper (only where the edge of a crystal could make good enough contact with the dry paper and some of it remain on the paper long enough for the reaction on the paper to occur.
The pathways on the HazCat Charts were written based on color changes that occurred on the paper within 5 secs (using the technique: “add 2 drops of 3N HCl to the end of the paper, rub/stir the unknown on the watchglass vigorously for 3 seconds, lift the paper above the watch glass and observe it for another 2 seconds – make the observation now”). If the paper is left out exposed to the air it will change on it’s own and if you look at it say five minutes later it will have turned blue black. The paper has to be read in the first 15 seconds or so.
The HazCat system also uses the paper to gain information about substances that aren’t necessarily oxidizers but react with the paper in a distinct way when it is “activated” with the hydrochloric acid.
As stated already, the system can indicate certain transition metal salts, concentrated sulfuric acid, mercury compounds, bismuth nitrate, hydriodic acid, certain lithium salts, sodium borohydride, and certain reactive ammonium salts by their distinctive reaction with the oxidizer paper/hydrochloric acid when used as directed in the Hazcat System.
The paper is also used in the Thermal Oxidizer Test and the Oxidizer in Air Test.
There are powerful oxidizers that give a negative result on the paper (in the Oxidizer Test on the watch glass), these salts are identified with the Thermal Oxidizer Test. This test is done as part of the Thermal Analysis and checks for oxidizing gases that are released as a result of pyrolysis of the unknown. It consists of taking a piece of KI starch paper, activating it with the 3N HCl and dipping it into the head space vapors to see if oxidizing gases have been released from the substance during it’s thermal decomposition. Substances such as ammonium nitrate, potassium chlorate, ammonium perchlorate that give a negative result on the watch glass will give a positive during the Thermal Oxidizer Test.
The Oxidizer Test paper turns blue-black whenever the paper comes into contact with an oxidizer that is an equal or stronger oxidizer than iodine. If the substance is able to oxidize the potassium iodide that is on the paper it will form elemental iodine (I2). This then will form the triiodide anion I3- (a soluble form of iodine) which then reacts with the amylose in the starch on the paper to form a blue-violet complex. In order for the test to work the oxidizer being tested has to be in aqueous solution. The potassium iodide on the paper has to be in solution as well in order for it to dissolve the iodine and form the triiodide. The paper, as sold by the manufacturer, can not be used “dry” on solids that are not in solution. Salts such as sodium perborate that have a low solubility, ~2% in water, will give a negative result if the oxidizer test paper is just wetted with distilled water. When the 3N hydrochloric acid is used to wet the paper the sodium perborate gives a quick positive result.
Determining if an oxidizer will produce a positive result on the oxidizer test paper is not as simple as checking a list of relative strengths of oxidizers to see if the oxidizer in question is stronger than iodine. Many other factors come into play. Properties such as the hydration enthalpy, the electron affinity, the water solubility, concentration and acid reactivity all will have an effect on the ability of the oxidizer in question to oxidize the KI on the paper. The limit of detection when used per the manufacturer’s directions (dry dipped into an aqueous solution) is 1 mg/l of nitrite anion in solution or 1mg/l free chlorine in solution. Fluorine, which is one of the strongest oxidizers is actually too strong of an oxidizer to cause a positive result because it oxidizes the water present before it can react with the KI on the paper.
Using the hazcat system and KI paper as directed in the kit, the substances listed in Table A below should give a positive Oxidizer Test. Some of these should be considered false positives, since they are not DOT oxidizers. Those highlighted in red would not be considered DOT oxidizers in the sense that they would enhance combustion. The fact that a substance tests positive on the Oxidizer Test should never be enough information to call the substance an oxidizer – complete identification is necessary. Never bulk one oxidizer with another since the stronger oxidizer can oxidize the weaker one leading to a vigorous exothermic reaction and container failure.
Table A: List of Substances that give a Positive Oxidizer Test
Substance Notes Concentration
ammonium dichromate aqueous solution, solid
ammonium persulfate aqueous solution, solid
benzoquinone is not DOT oxidizer, is a flammable solid
bromine in aqueous solution
bromine, chlorine or iodine dissolved in organic solvents, eg., carbon tetrachloride, ether and ethanol
calcium hypochlorite solid or aqueous solution (pool shock)
cerium oxide solid, technical grade, – not a DOT oxidizer – inert
chlorine in aqueous solution
chlorocyanurate, cyanuric acid
chromate salt aqueous solution, solid
cobalt thiocyanate aqueous solution, solid
copper sulfate aqueous solution, solid
ferric chloride aqueous solution, solid
gold chloride surprisingly gold is a stronger oxidizer than iodine
hydrobromic acid yellow or brown solution (color most likely due to dissolved Br2)
methyl ethyl ketone peroxide MEKP – (organic peroxide)
nitric acid > 20%
piranha base mixture of hydrogen peroxide and ammonia
platinum chloride aqueous solution
potassium chlorate Solid that has become exposed to heat or has “aged” in storage
potassium chromate aqueous solution, solid
potassium dichromate aqueous solution, solid
potassium ferricyanide aqueous solution, solid
potassium nitrate solid that has become exposed to heat or has “aged” in storage
potassium permanganate solid or aqueous solution
prague powder curing salts containing ~ 6% sodium nitrite – not a DOT oxidizer
sodium hypochlorite solid or aqueous solution (household bleach)
sodium perborate aqueous solution, solid
sodium percarbonate aqueous solution, solid
sodium persulfate aqueous solution, solid
tincture of iodine
Table B: Substances that may give a positive result – not yet tested
Yet to be tested
ascaridole organic peroxide found in tonic drinks and as a food flavoring – paico powder
sodium metavanadate vanadium salt
various other organic peroxides: t-butyl hydroperoxide, ethyl hydroperoxide, diacetyl peroxide
Table C: Substances that give a false result – and yet are strong oxidizers
These compounds are identified during the Thermal Oxidizer Test
Hydrobromic Acid is an example of a substance that can cause confusion. Depending on its age, if it has been exposed to light or heat it can give different results in the Oxidizer Test. The Hazcat System identifies Hydrobromic acid on the Liquid Acids Chart on both paths (negative oxidizer path and positive oxidizer path). Reference sources state:
Wiser: toxic and corrosive – store away from oxidizers
Cameo Chemicals: corrosive – incompatible with oxidizing agents: perchlorates, peroxides, permanganates, chlorates, nitrates, chlorine, bromine, fluorine
When completely pure, hydrobromic acid is a clear liquid. As it ages and/or is exposed to light it takes on a yellow to brown color. This is most likely due to some complex chemistry that involves dissolved free bromine, the formation of hypobromous acid and bromic acid. Bromine has a 4% solubility in water. Hypobromous acid HOBr is a bleach and an oxidizer. Bromic acid (HBrO3) only exists in aqueous solution. It is a colorless solution that turns yellow at room temperature as it decomposes to bromine. Bromic acid is a powerful oxidizing agent. While technical grade/aged hydrobromic acid is not a DOT oxidizer, it will most likely give a positive Oxidizer Test and will be reactive towards reducing agents.