[Histonet] picric acid

Morken, Timothy Timothy.Morken at ucsf.edu
Fri May 6 10:27:41 CDT 2016

Julio, you can just pour water into the container. We always oversaturated so that a layer of water was on top of the powder. 

Look at this explanation 

or read the text below if you cannot open this.  This contains instructions on how to properly store picric acid powder, and how to deal with dry powder found in the lab.

Long ago I had the pleasure of discovering a batch of six 2kg bottles of dry picric acid in our "bunker" where we stored flammables. Over 10 years old according to dates on the box. We called in the fire department to take care of it. They hosed it down, removed it and disposed of it; how, I don't know. 

Tim Morken
Pathology Site Manager, Parnassus 
Supervisor, Electron Microscopy/Neuromuscular Special Studies
Department of Pathology
UC San Francisco Medical Center

Mark Cameron, CIH
Every couple months, an article appears in the local paper about a bomb disposal team removing picric acid that was found in a laboratory. The material is usually taken to be blown up. So why is picric acid considered so dangerous? Well, let’s look at the history of the use of Picric Acid and see what can be done to avoid those types of situations.

Picric Acid (2,4,6 Trinitrophenol) is frequently found in forensic laboratories for use in the Christmas Tree stain (1) and for Urine detection (2). Histology uses include connective tissue stain (Jullien’s picroindogocarmine and Van Gieson’s picro-acid fuchsin), cytoplasmic stain (Van Gieson’s with iron hematoxylin), woody sections (picro aniline blue) and as a fixative agent (3). It was used in medicinal formulations in the treatment of malaria, trichinosis, herpes, smallpox and antiseptics. A one- percent solution was also used in the treatment of burns (4).
British Chemist Peter Woulfe discovered picric acid in 1771. Picric acid was named from the Greek word pikros, which means “bitter” due to its bitter taste (5). It was used to dye silk and wool yellow. Workers making picric acid during World War I were called “canaries” because their skin was stained yellow (6).

The explosive characteristics of Picric acid were discovered early. In 1885, experiments with picric acid were conducted in Lydd, England and the English adopted it as an explosive material called Lyddite in 1888. It was used extensively in bombs and grenades during World War I (7). Anhydrous Picric acid is similar to TNT. It needs usually needs a “booster” such as a primer to create the explosion. However, as a strong acid, picric acid attacks common metals (except tin and aluminum) creating explosive salts, which are shock-sensitive. Bombs, mines and grenades were coated with tin or ashpatim to prevent the picric acid from contacting the metallic shell (8).

Several catastrophic events involving picric acid have occurred. On December 6, 1917, an ammunition ship in Nova Scotia carrying 2,300 tons of picric acid as well as 400,000 pounds of TNT caught fire and exploded. Over 1,900 people were killed immediately and 9,000 were injured (9). Shock-sensitive metal picrates demonstrated their hazardous nature on May 1, 1916 when a fire at a French ammunition factory caused molten picric acid to flow onto the concrete floor. Calcium picrate was formed and detonated, killing 170 people (10).

Have there been any explosions in laboratories? There are no documented instances of spontaneous detonation of picric acid in a laboratory (11). The Department of Transportation classifies Picric Acid (Trinitrophenol) with less than 30% water by mass as a Class 1.1D explosive; with greater than 10% water by volume, it is a class 4.1 flammable solid (12). In the wetted state, it is unlikely to be an explosive hazard. If a bomb squad tries to blow it up, the picric acid will not detonate (13) and will just spread picric all over the area!
The big concern has been with finding dehydrated picric acid. The most dangerous situations is if the bottle is old and has a metal cap. Under these circumstances, shock sensitive metal picrates may have formed on the cap contact area. Explosive experts should be contacted under these situations. Knowledgeable bomb disposal experts will use a robot to pick up the container and place it in water to re-hydrate the material (14) or remove it for detonation elsewhere.

If a plastic cap is present, and the acid inside has dried, some crystals may be on the threads and the friction of removing a plastic cap might be enough to detonate the container. Under these circumstances, the container may be safe enough to place in a pail of water. Submerge the bottle to allow water to enter the cap and threads and dissolve any crystals that might be on the threads. Add ice to cause shrinkage of the bottle to enhance penetration of the water. Leave it like this for several days, until water can be seen inside the bottle. At this point, it is safe to open the cap and re-hydrate the acid inside (15). Whenever in doubt, contact explosives experts.
Of course, an ounce of prevention is worth a pound of cure. If you really need to have picric acid in your lab, here’s what you should do:
Make sure that the picric acid is kept wet! Do not open a new bottle until needed. Then date the container to show when it was first used to help you in a routine inspection program. As part of your lab inspection program, check the hydration of your picric acid at least every six months and add distilled water as necessary.
Do not use metal spatulas to remove the material.
Be sure to clean the bottleneck, cap and threads with a wet cloth before resealing (16).
Get rid of old bottles with metal caps
Do not store large amounts of picric acid. Dispose of your picric acid every two years (17).
If possible, eliminate it from your inventory by purchasing premixed stains or a 1% solution for using in stain preparation.
If you decide to dispose of your wet picric acid, several options are available. First, you could try reducing the picric acid to a non-explosive form using sodium hydroxide and sodium sulfide (18). After this treatment, the material will still be toxic and have to be
disposed of as hazardous waste. Alternatively, it could be manifested as a flammable solid for hazardous waste and disposed of by incineration. DO NOT pour it down the drain; it could react with copper or iron piping to form the explosive salts.
As a last consideration, Picric Acid is toxic. Ingestion of 1-2 grams would cause severe poisoning. The dust is irritating to the skin and eye. A peculiar effect on the eye is “yellow” tainted vision. Systemic poisoning causes headache, vertigo, nausea, vomiting and diarrhea. The skin will turn yellow in severe exposures. Red colored urine may be produced (19). These symptoms would not expected in the laboratory environment under traditional uses.

Gaensslen, R., Mertens, J., Lee, H., Stolotow, M., “Staining and Extraction Techniques”, Proceeding of a Forensic Science Symposium on the Analysis of Sexual Assault Evidence., FBI Academy, 1983.
Slot C. “Plasma creatinine determination. A new and specific Jaffe reaction method.” Scand J. Clin. Lab. Invest. 1965, 17: 381
Lillie, R.D., “H.J. Conn’s Biological Stains”, Williams & Wilkins Company, 1969, Baltimore, MD, pages 5, 60-61.
Patty’s Toxicology, John Wiley & Sons: New York, 2000, Volume IIB, page 980.
Davis, Tenney, “The Chemistry of Powder and Explosives”, Angriff Press, 1984, page 164.
Hamilton, Alice, “Exploring the Dangerous Trades”, American Industrial Hygiene Association: Fairfax, Virginia, 1995, page 185.
Cooper, Paul, “Explosives Engineering”, Wiley-VCH, 1996, page 33.
Davis, ibid.
Phifer, Russell, “Picric Acid: When is Panic Justified?”, Speaking of Safety, Volume 9, No. 2, 2000, page 1-3.
Medard, Louis, “Accidental Explosions, Volume 2: Types of Explosive Substances”, John Wiley and Sons: New York, 1989, page 739.
Phifer, ibid.
Code of Federal Regulations, Title 49, Section 172.101.
Kraut, Irv, In Handbook of Chemical Health and Safety, Alaimo, Robert J., Ed., Oxford University Press; New York, 2001, page 406.
Personal Communication with Tom Gundlach of RHR Inc., August 23, 2000.
Guidance for the Management of Reactive Chemicals, Picric Acid, http://www.uwsa.edu/oslp/ehs/info/picric.htm , 8/97 revision.
Safe Use and Management of Picric Acid, Safety Net #104, http://wwwehs.ucdavis.edu/sflynet/sn-104.html ,11/21/01
Biological & Chemical Safety Code, Appendix H-3, Handling Procedures for Unstable Agents, University of Saskatchewan, Department of Health and Safety, http://duke.usask.ca/~whiterv/unstable.html, 11/21/01.
Lunn, George and Sansone, Eric B., “Destruction of Hazardous Chemicals in the Laboratory”, John Wiley & Sons: New York, 1990, page 219-221.
Documentation of the Threshold Limit Values, American Conference of Governmental Industrial Hygienists, Inc.: Cincinnati, Ohio, 1991, page 1271.

-----Original Message-----
From: Julio Benavides via Histonet [mailto:histonet at lists.utsouthwestern.edu] 
Sent: Friday, May 06, 2016 7:11 AM
To: histonet at lists.utsouthwestern.edu
Subject: Re: [Histonet] picric acid


For how long can you keep it in water? any particular dilution or just keep it humid (saturation)?

We also do have some dry picric acid in the lab and, after reading about the bomb squad, I was begining to get concerned...

Thanks a lot


El 06/05/2016 a las 15:30, Rene J Buesa via Histonet escribió:
> Picric acid is an expensive reagent useful in many histology 
> procedures.The advise you received of adding water is a good one.Humid 
> picric acid will not explode at all. Why waste a good reagent?Keep 
> humid, you will eventually used it.René
>      On Thursday, May 5, 2016 3:24 PM, Mca Werdler via Histonet <histonet at lists.utsouthwestern.edu> wrote:
>   Dear histonetters,
> Since a few months, i started working in a histology lab, run only by 
> me ( coworkers are not specialized in histology). There has not worked 
> here a person at histology for about 2 years.
> After many new protocols, i decided to clear out some chemicals.
> Now i found around 1 KG of DRY picric acid. I informed my coworkers 
> about this, and they said just to dissolve everything in water.
> What do you guys think is the best way for handeling with this 
> explosive chemical? Thank you all in advance!
> Maarten
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