CHEMICAL DATA NOTEBOOK SERIES #60: PICRIC ACID
HAZARDOUS MATERIALS
Picric acid is an explosive, reactive, oxidizing, corrosive, toxic, pale yellow, crystalline solid with a bitter taste, it is a Class A explosive and is used in the manufacture of other explosives, batteries, colored glass, dyes, matches, pharmaceuticals, and photographic chemicals. It may be shipped and/or stored as a wet mixture containing no less than 10 percent water.
PROPERTIES
In its crystalline form, picric acid is very sensitive to heat and shock. It melts at 252°F and detonates at 572°F. Some references list an autoignition temperature of 572°F, and this is technically correct. Be aware that it ignites explosively, which means it explodes at 572°F. At least one reference lists a flash point of 302°F, and this also may be correct. Do not assume that you are dealing with a combustible liquid because this flash point is listed. Picric acid has a specific gravity of 1.76, a molecular weight of 229, and a vapor density of 7.89. It is slightly soluble in water. Its chemical formula is 0⅞^02)⅝011, which sometimes is written as 0⅛11^⅞07–
The molecular structure of picricacid is:
The OH at the top of the hexagonal benzene ring is the hydroxyl radical. When there are no “nitro” radicals (NO,) attached to the benzene ring, the resulting structure is known as phenol. Hence, the three nitro groups make it trinitrophenol. If the (ill, or methyl group were substituted for the hydroxyl group in the picric acid molecule, the name of the compound would be trinitrotoluene, or TNT. This should remind emergency responders that picric acid’s main hazard is as an explosive—not a corrosive.
HAZARDS
I cannot repeat enough —from the perspective of safety—that picric acid’s main hazard is its function as an explosive. More members of a firedepartment than of the hazardous materials response team may become involved with picric acid. Every June many fire departments respond to a local high school’s request to dispose of chemicals from the chemistry lab. It seems that every high school chemistry lab in the United States has or has had picric acid among its reagents. One source indicates that this may be due to the fact that the U.S. government had a tremendous stockpile of picric acid after World War II and that it either sent unsolicited samples of it out to schools or high school chemistry teachers heard about its availability and requested samples. In any event, most of the material wasn’t used because it was too dangerous; it sat around in its containers and slowly dried out and crystallized. Some of these containers are showing up now—43 years later, and you can imagine their condition! I still hear stories about picric acid samples being found in high schools, so beware!
Picric acid will detonate at 572°F, well within the energy range of all normal ignition sources. As a dry material, picric acid is classified as a high explosive. High explosives are characterized by their re/atire insensitivity to heat and shock. Even though picric acid has been classified in this way, it should not be considered insensitive to anything.
Other high explosives such as the aforementioned TNT may be subjected to a great deal of shock and even be consumed by fire without exploding. The same cannot be said for picricacid; it detonates when it is ignited.
File oxidizing capabilities of picricacid might be the reason it is insensitive to heat. When mixed with “ordinary” combustible material, it reacts like an oxidizer and makes the other material highly dangerous. Such a mixture burns fiercely, and the threat of an explosion due to the presence of the picric acid in the mixture is always there. Even when shipped or stored in its “wet” form, picric acid acts as an oxidizer, ready to support combustion whenever it is subjected to heat. Of course, the oxidizing hazard gives way to the danger of a potential explosion when enough heat is present.
Picric acid is corrosive and causes burns to human tissue. It also corrodes common metals, probably through its oxidizing action, but it also may form explosive compounds with those metals. Reference materials for explosives state that picric acid attacks all common metals except aluminum and tin. This indeed is a corrosive reaction, and the products formed by this reaction are usually unstable, explosive compounds.
Picric acid is also a toxic hazard. Its TLV/TWA (threshold-limit value/timeweighted average) is 0.3 mg/m’ (milligrams or thousandths of a gram per cubic meter of air). Its STEL (shortterm exposure limit) is 0.1 mg/m’ for 15 minutes. Its 11)1.11 (immediately dangerous to life and health) is 100 mg/m’. It is toxic if ingested or absorbed through the skin. If ingested, it will cause such symptoms as nausea and vomiting, depression of the central nervous system, hypothermia, toxic hepatitis, unconsciousness, and death.
It has been assigned a “4” in the flammability quadrant of the NFPA 704 hazard rating system—a rating usually reserved for liquids with low flash points, low ignition temperatures, and wide flammable ranges such as ethyl ether (Fire Engineering, April 1991). This rating was given to picric acid because there is a great danger of explosion if it is ignited. The “4” does not qualify picric acid to be classified as a flammable liquid. There are enough misconceptions about this high explosive as it is.
Picric acid also has been assigned a “4” in the reactivity quadrant. It is reactive with many materials and forms explosive, unstable salts (picrates) with ammonia, bases (inorganic compounds containing the hydroxide (OH ‘) ion, carbonates (inorganic salts containing the COj~2 ion), concrete, other oxidizers, and metals such as copper, lead, mercury, and zinc. It reacts with all common metals except dry aluminum and tin. When mixed with wet aluminum, the mixture ignites by itself, usually after a short delay.
The reactivity with lead is so fast and dangerous (lead picrate is very unstable and dangerously explosive) that lead and all compounds of lead are strictly forbidden in any areas where picric acid is manufactured, stored, or used. The reactivity with other metals is also very fast: Whenever it contacts a metal, a picrate that deflagrates or detonates forms and in turn detonates the picric acid. If all the available picric acid converts to picrates before the explosion, the resulting detonation is several times more powerful.
The picric acid reacts with the carbonate ion in metallic carbonates to form hydrated picrates of varying explosive power. It is best to prevent picric acid’s contact with any carbonates. Picric acid reacts with concrete because the aggregate in concrete is limestone, which is calcium carbonate. Any work area where picric acid is manufactured, stored, or used should not have a concrete floor.
Any chemical compound containing the word “picrate” in its name should be considered an explosive. The picrates, as a group, are more powerful explosives than picric acid. Ammonium picrate is used as the explosive in armor-piercing shells.
Most picrates are highly toxic as well as highly sensitive explosives. None of the picrates should be heated to temperatures near 400°F for fear of detonation; many also w’ill liberate the toxic oxides of nitrogen at those temperatures.
NONFIRE RELEASE
Release of picric acid in any amount must be considered hazardous. Even small amounts will recrystallize as they dry’ out, and any friction will cause the material to explode.
At the first indication of a release, contact the proper environmental authorities. If a large container or shipment of picric acid is involved in an accident, activate the community’s emergency response plan as dictated by SARA TITLE III. Also, immediately notify’ the manufacturer.
Evacuate immediately. The radius of evacuation depends on the amount of material involved in the incident, not just the amount spilled. The area should be as wide as it would be for any other dangerous explosive, including distances within which broken windows may be a problem. A radius of two miles is not out of the question for large amounts.
Constantly remind emergency responders that they are dealing with an acid that is a real, honest-to-goodness high explosive and not just a corrosive. Apprise responding agencies of the hazard of a potential explosive anil that evacuation must be carried out as if the same amount of dynamite or TNT were involved. Secure the immediate area and remove all sources of possible ignition. Resist the temptation to sweep up and/or shovel the spilled material, as the resulting friction may cause ignition and detonation. This is another example of why emergency responders should not be involved in salvage or cleanup operations. Relegate these responsibilities to the manufacturer, the buyer, the shipper, or professional salvage companies.
Picric acid is very seldom shipped as a dry product; it more likely is wet with water at no less than 10 percent. Some products are shipped between 10 percent and 30 percent water, while occasionally a shipment contains more than 30 percent. This material is shipped as a flammable solid. Whatever the amount of water present with the picric acid, it can evaporate and will leave behind the dangerous yellow crystals of pure picric acid.
Some references claim that picric acid is as stable as or just slightly less stable or sensitive than TNT. The stability of TNT is legend. Military officers lecturing on explosives to a new class of recruits often take a slab or package of TNT and slam it down on the desk of a student who has dozed off. This gets the attention not only of the sleeping recruit but of everyone else in the class.
This should not be done with picric acid. Regardless of how many experts claim that picric acid is a high explosive-anil therefore relatively insensitive to heat and shock—don’t take chances with your life and the lives of others. Picric acid is much more reactive than TNT and therefore may have become contaminated with picrates or something else that can detonate it. Picric acid, in its dry form, is very dangerous and is reactive enough in its wet form to be considered just as dangerous.
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
88-89-1
STCC
(Standard Transportation Commodity Code)
4917120
RTECS
(Registry of Toxic Effects of Chemical Substances)
T)7875000, dr>’ material
TJ7885000, material wet with 10 percent water TJ7877000, material wet with from 10 to 30 percent water
UN/NA
(United Nations/North America)
0154 and 1344
DOT
(U.S. Department of Transportation)
Class A Explosive
NFPA 704 Rating
2-4-4
Isolate any release of picric acid as quickly as possible. A spill should be safely covered if possible. Remember, since picric acid burns and supports combustion, just about any contaminant increases the possibility of explosion. Do not allow picric acid to contact equipment or tools made from metals that will react with it.
Prevent picric acid from entering sewers and waterways. The large quantity of organic matter in a sewer provides oxygen with which it can react. An ignition source will produce a fire at best and a detonation at worst. Many sewer pipes are made of concrete, and the picric acid may react with the calcium carbonate in the aggregate to form explosive calcium picrate. Promptly warn the sewage treatment facility if picric acid enters a sewer system.
Picric acid entering a waterway threatens aquatic life. If the waterway is a river or stream, notify all downstream users immediately. Consult the manufacturer about neutralization techniques. The environmental authorities will monitor the water to determine when it is safe to use. Any water contaminated with picric acid and used to cool equipment in an industrial operation may evaporate, leaving the picric acid behind. This will develop into a potentially explosive situation.
The manufacturer, buyer, or shipper may have expert advice and help available. Certainly one of them will provide professionals to perform salvage and cleanup tasks. Emergency responders should not clean up or salvage such a dangerous material after the incident has run its course — nor should this be expected of them.
FIRE SCENARIO
When threatened by the heat of a fire, picric acid may detonate at any moment. The material, even in the wet state, may burn, and the combustion may evolve to an explosion quite rapidly. Cool any container holding picric acid in any form by delivering water from as far away as possible; do this, however, only if no lives, including those of emergency responders, are in danger. If this cannot be done, withdraw all personnel and protect exposures. Do not get caught between the fire and the container threatened by heat.
If the picric acid is already burning, do not attempt to fight the fire. Employ instead the techniques for handling explosives in a fire situation — withdraw and protect exposures. If the manufacturer sends a special team to assist, it will recommend that the fire not be fought.
PROTECTIVE EQUIPMENT AND CLOTHING
Materials impervious to and nonreactive with picric acid offer protection. Full face shields, chemical splashproof goggles, rubber gloves, and rubber boots offer some protection. Wear positive-pressure, self-contained breathing apparatus.
As far as total encapsulating suits are concerned, the references do not agree on the material that offers protection. One reference states that substantial data show that rubber (probably natural rubber) offers good resistance and that limited data support neoprene, nitrile rubber, and nitrile/ rubber/polyvinyl chloride as materials offering good resistance. Another reference says that natural rubber, neoprene, and nitrile rubber provide good to excellent protection. A third reference states that natural rubber and nitrile rubber are questionable at best, but that natural rubber is not recommended for long exposures.
SYNONYMS
carbazotic acid
2-hydroxy-1,3,5-trinitrobenzene Melinite
nitroxanthic acid Pecral
phenol trinatrate picronitric acid trinitrophenol
1.3.5-trinitrophenol
2.4.6-trinitrophenol
Protection from hazardous materials is relative. It depends on the thickness of the protective material, the integrity of the seams, the concentration of the product, and the length of exposure time. Consult the manufacturer of the protective suits and the manufacturer of the picric acid.
FIRST AID
If picric acid is inhaled, remove the victim to fresh air. If the victim has stopped breathing or breathing has become difficult, administer artificial respiration (mouth-to-mouth resuscitation may expose the first-aid provider to the material in the victim’s mouth or vomit). Provide medical attention immediately.
Do not induce vomiting in victims who have ingested picric acid. Call for immediate medical attention whilemaking sure the victim is warm and comfortable.
For skin contact, remove all contaminated clothing and wash all affected body areas with large amounts of water and mild soap or detergent solution. Seek immediate medical attention.
If picric acid contacts the eyes, immediately flush them with largeamounts of water or normal salinesolution for 1 5 to 20 minutes; lift the eyelids occasionally. Call for medical attention immediately.
