Recognition and safemanagement of explosivechemicals

By David Blair andScott Zimber

INTRODUCTION

Identifying potentially explosivechemicals and understanding thehazards associated with them re-

duces the risks inherent to their stor-age and use. Mishandling these chem-icals has proven all too often to causeserious damage to property and per-sonnel, and even loss of life. Many ofthese chemicals are used and managedevery day in manufacturing industries,research and development laboratories,educational institutions, and chemicalwaste management companies.

An explosive chemical may be de-fined as a material that, when exposedto some type of initiation, undergoes asudden, violent change, releasing ex-cessive energy. Initiators include heat,shock, friction, light, and contamina-tion from noncompatible material.These initiators can cause an explo-sion individually, or in concert witheach other. Controlling the initiatingelements is a vital part of any explo-sive chemical management program.

Determining which chemicals havethe potential for explosion is the firststep in understanding the risks associ-ated with chemical inventories.

PEROXIDE-FORMING COMPOUNDS

The peroxidation or autoxidation pro-cess, as some would describe it, in-volves the incorporation of molecularoxygen -O-O- at certain chemicallysusceptible sites in the structure of thechemical. Most peroxide-formingchemicals build up hazardous levels ofperoxides as the peroxidization inhib-itor, added by the chemical manufac-turer, expires. Another way to buildup peroxide concentrations is throughliquid concentration as the containeris opened and the liquid level is re-duced, or when the solvent is beingdistilled which, by process, concen-trates the peroxides already presentinto a decreasing liquid volume. Be-fore distilling a peroxidizable solvent,the level of peroxides should bechecked to prevent an unwanted ex-plosion. If the peroxide levels are rel-atively high, the peroxides should beremoved prior to the distillation.

Uninhibited peroxide-forming chem-icals, especially monomers, present anadditional level of risk. Uninhibitedperoxide formers, such as most high-performance liquid chromatography(HPLC) grades of peroxide-formingsolvents, mandate a closer control ofinventory to ensure the solvent is usedup quickly and not allowed to accu-mulate in storage, especially after thecontainer is opened. Chemical manu-facturers produce some peroxide-forming solvents without inhibitorsbecause of the interference potentialwith the UV detection of eluted species.

Uninhibited monomers, whichreadily form peroxides, should be usedup within 24 hours, or, after checkingthe peroxide concentration, have an in-hibitor added. Additionally, inhibitors

added to a peroxide-forming solvent ormonomer will not reduce the level ofperoxides already formed; any perox-ides already formed must be chemicallyreduced or removed, which is not thefunction of an autoxidation inhibitor.

Some peroxide formers warrantspecial mention. Diisopropyl ether,for example, readily forms peroxidesbuilding up to hazardous levels with-out the effect of concentration, andhas been known to produce explo-sions just on standing over time. Anunopened container of isopropyl etherwith inhibitor should not be storedlonger than three months; openedcontainers should be used or properlydisposed within three days.

Another unique management prob-lem occurs with an empty containerthat has previously contained a perox-ide-forming chemical. Many explo-sions, and serious injuries to person-nel, have occurred when an emptycontainer that has previously con-tained ethyl ether was subjected evento normal, careful handling practices.Explosions from peroxide formers arecharacterized by one or more “pops,”a bright flash, and dispersion of shrap-nel from the container. Secondaryfires and explosions from surroundingchemical inventories are a real con-cern. A professional high-hazard man-agement technician inadvertently det-onated an “empty” ether containerwhile attempting to verify its status.The technician received no bodily in-juries due to the exceptional level ofpersonal protective equipment usedby the technician. Any container thathas held a peroxide-forming chemicalshould be triple rinsed with anothernon-peroxidizable, compatible sol-

David Blair and Scott Zimber areemployed by Environmental andTechnical Specialists (ETSI), locatedin Olympia, WA, and Rockford, IL,respectively. ETSI maintainsmembership with the EnvironmentalAssessment Association and theNational Fire Protection Association(not Agency).

14 © Division of Chemical Health and Safety of the American Chemical Society 1074-9098/00/$20.00Published by Elsevier Science Inc. PII S1074-9098(00)00076-9

FEATURE

vent, or even water, before the con-tainer can be considered safe and trulyempty. Each container should beclearly marked with a date and signa-ture verifying its status. Rinsates shouldbe disposed properly since they do con-tain the original chemical as well.

Metals and PeroxidesPeroxide-forming solvents are not theonly chemicals capable of forming aperoxide structure. Potassium metal,and to a lesser degree, sodium metal,are both capable of forming superox-ide layers on the surface of the metal.These superoxide layers are detectedby their colors yellow and/or orange,and even red for extreme cases of su-peroxide formation.

Sodium and potassium metal arenormally stored under oil or hydrocar-bon solvent to deny contact with oxy-gen in the air. If the oil level is re-duced, or the hydrocarbon solvent isallowed to evaporate, exposure to ox-ygen in the air can result in the forma-tion of a superoxide layer on the sur-face of the metal. When thesuperoxide layer is formed on the po-tassium or sodium metal, the con-tainer should not be handled withoutspecial protection because the super-oxides of potassium and sodium areknown to be shock-sensitive and po-tentially explosive. Some compoundsof sodium and potassium, such as so-dium and potassium amide, are alsonoted for forming superoxides.

OTHER EXPLOSIVE CHEMICALSExplosive chemicals are not just lim-ited to peroxide-forming materials.Many other chemicals are potentialexplosion risks, and some of them areworth noting.

Multi-nitro-aromatic compounds,such as picric acid and hexanitrodi-phenylamine, found application astrue military type explosives. Most ofthese chemicals are shipped with var-ious percentages of water as a stabiliz-ing agent. If the chemical is allowed todehydrate, the now dry multi-nitro-ar-omatic is both friction and shock sen-sitive. Just twisting the cap with mate-rial in the threads or concentrated inthe lid area is enough to initiate anexplosion. In storage and use, these

chemicals therefore should always bemonitored to make sure they are keptin a water-wet condition.

Many chemicals are safe in normaluse and storage; however, if thesechemicals are allowed to come intocontact with another metal-bearingcompound, a potentially explosive sit-uation can result. This category ofchemicals includes the azide and per-chlorate families of compounds. So-dium azide solutions washed downthe drain in laboratory sinks contain-ing lead or copper plumbing have re-sulted in numerous explosions duringroutine maintenance or the removal ofthe dried out plumbing fixtures. Theformation of the corresponding metalazide is the cause of the explosions.Heavy metal azide compounds are no-toriously shock-sensitive and poten-tially explosive chemicals, especiallywhen allowed to dry out.

Sodium and potassium perchloratesare also not considered shock-sensi-tive chemicals in normal use and stor-age. However, if these chemicals areallowed to come into contact with an-other metal-containing compound,the combination can produce heavymetal perchlorates that are consideredshock-sensitive, potentially explosivechemicals. Numerous incidents are re-corded where organic perchloratepreparations being transferred to stor-age containers using a metal spatulacaused an explosion. A chemist from ahazardous waste management com-pany lost a thumb and seriously dam-aged other digits and face while at-tempting to transfer magnesiumperchlorate using a metal instrument.Most multi-nitro-aromatic com-pounds also form extremely shock-sensitive, and potentially explosive,combinations with metal-bearingcompounds. For instance, the verywell-known chemical, picric acid, incombination with metals, or metal-bearing compounds, has producednumerous explosions. One of the earlyuses of picric acid was in military or-dinance. However, when the metalcasings of the ordinance came intocontact with the high-explosive picricacid, many unwanted, and oftencostly, explosions were the result.

Familiarizing chemical handlerswith the risks associated with various

reactive chemicals is a key step in re-ducing the potential for an explosion.The next steps provide workers withimportant tools and guidelines to han-dle the now identified chemicals.

PROPER MANAGEMENTProper management for potentially ex-plosive chemicals must have four ma-jor elements. These elements are: in-ventory control, proper storage andusage, peroxide test scheduling andvisual inspections, and crisis plan-ning. Detailed preparation and exe-cution of these four elements are vi-tal for minimizing risks that couldlead to explosions.

Inventory ControlMany institutions use technology suchas bar coding to track the movementof chemicals in and out of their pro-grams. This approach and similar onesare effective in controlling inventoriescontaining explosive chemicals. Chem-ical managers should record the chem-ical acquired, amount per container, ex-piration date, date received, and areawhere the chemical is being used. Thisinformation is the benchmark for inven-tory control. Additionally, control num-bers and receiving dates should be lo-cated on each container. Containersof peroxide-forming chemicals shouldalso have labels indicating date re-ceived and peroxide test dates.

Many programs place markings oneach potentially explosive containerclearly indicating that it must be usedcarefully and stored properly. Fluores-cent stickers or dots placed on con-tainer lids, shoulders, or labels alertchemical handlers that these itemsneed special attention when in-use ortemporarily stored.

Storage and UseCareful storage of potentially explo-sive chemicals reduces the potentialfor an explosion. Proper storage is im-portant for all chemicals; however,special attention should be paid toperoxide-forming chemicals. Perox-ides are more readily formed whenthese chemicals are exposed to air,light, and temperature variances. Per-oxidizable chemicals should be storedin amber bottles, or other containersthat reduce exposure to light.

15Chemical Health & Safety, May/June 2000

Containers should remain tightlysealed, restricting oxygen from enteringthe container. In many cases, contain-ers of peroxide-forming chemicals areshipped from the supplier with a blan-ket of an inert gas such as nitrogen orargon above the liquid. Once in use,replacing the nitrogen or argon coverover the chemical prior to closing thecontainer will significantly slow the for-mation of peroxides. However, for mostmonomers, in order for the inhibitor tobe effective in preventing the buildup ofperoxides, the atmosphere above theliquid must contain some oxygen.

Long-term or even temporary stor-age of peroxide-forming chemicals inrefrigerators or cold rooms should bediscouraged. For most peroxide form-ers, refrigeration causes the inhibitorto be ineffective in retarding the for-mation of the free radicals, which re-sults in autoxidation and peroxide for-mation. Also, removal of containers ofperoxide formers from long-term stor-age in a refrigerator has resulted inexplosions due to the rapid tempera-ture change and thermal shock to al-ready formed peroxide structures. Ad-ditionally, some easily peroxidizablechemicals will freeze in a cooler temper-ature; for example 1,4-dioxane freezesjust below room temperature. Freezinga container of 1,4-dioxane with an al-ready high level of peroxides could re-sult in an even more unsafe condition.

Visual Inspections and PeroxideTestingOnce a container of a peroxide-form-ing chemical has been opened, it isimportant to regularly monitor for thepresence of peroxide structures andconcentration levels. Before moving acontainer of a peroxide-formingchemical, look for any signs of theformation of peroxide crystals. Whenpossible, use a soft, white light to in-spect glass jar content by back lightingthe jar and looking through the con-tents at the light on the other side.Notice any solid structures within thecontainer, including evidence of spi-der web–like features. Often, peroxidecrystals form on the exterior of a con-tainer, especially in the cap or lid re-gion. If a visual inspection reveals thepresence of solid peroxide structures

inside or on the exterior of the con-tainer, do not attempt to quantify theperoxide concentration—a very realexplosive potential already exists.

In addition to inspecting peroxideformers, pay close attention to otherreactive chemicals, such as metallicsticks. Make sure that they are fullycovered with mineral oil, or any othercover liquid used to keep them freefrom oxygen. Look for any evidence ofdrying, or contamination.

Once the container has been visu-ally inspected, check the log or in-spection label on the container tomake sure that it has been recentlymonitored according to an establishedschedule. Remember, opened con-tainers need to be inspected more of-ten than unopened containers due tothe introduction of oxygen.

There are two common ways to testperoxide-forming chemicals for con-centration levels. The easiest proce-dure is to use peroxide test strips avail-able through Aldrich and otherchemical distributors. Be sure to usestrips that have an upper concentra-tion range of at least 100 parts permillion. Strips are available with anupper range of 25 parts per million;however, since the quantification ofthe strip maximizes out at 25 parts permillion, the user will be unaware ofthe true concentration level of the ma-terial. There is a significant risk in-crease between a peroxide concentra-tion level of 25 ppm and 75 or 100ppm. Additionally, carefully followthe directions for use accompanyingeach container of test strips. Eachbrand of strips has different proce-dures in order to obtain effective andaccurate results.

Some peroxide-forming chemicalsdo not react properly to the colorimet-ric indicators of a peroxide test strip.Good testing technique would also re-quire the use of a back-up, confirma-tory test such as the KI Starch test asdescribed in the Davies article listed inthe bibliography.

Crisis PlanningIt is important for chemical handlersto know what to do in the event thatthey find or suspect a problem duringtheir inspections. Protocols differ from

facility to facility; however, there aresome consistent actions that should beapplied. First, immediately deny accessto the suspect container and clearlymark the container (with the leastamount of physical disturbance of thecontainer) indicating that it should notbe used or even moved. This is espe-cially important if peroxide crystals orsolid contamination are identifiedthrough visual inspection. Second, re-move other chemicals from the area inwhich the suspected problem containeris located only if this can be done with-out moving or disturbing the suspectcontainer. Make sure that all chemicalhandlers working in the area are awareof the container and potentially explo-sive nature of the problem.

Unless trained and properly pro-tected personnel are available at thefacility holding the problem container,get professional assistance in stabiliz-ing the situation. The National SafetyCouncil offers some guidelines inPamphlet I-655, or ask your hazard-ous waste contractor to suggest a pro-fessional company that specializes inhigh hazard remediation.

Bibliography1. Recognition and Handling of Peroxi-

dizable Compounds; National SafetyCouncil, Data Sheet I-655, Rev. 1987.

2. Kelly, R. J., Review of safety guidelinesfor peroxidizable organic chemicals.Chem. Health Saf. 1996, 3(5), 27–36.

3. Perchloric Acid; National Safety Coun-cil, Data Sheet I-311, Rev. 1982.

4. Approaches for the Remediation ofFederal Facility Sites Contaminatedwith Explosive or Radioactive Wastes;USEPA, Office of Research and Devel-opment, EPA/625/R-93/013, “ReactiveChemical Handling,” section 5.3.4,Sept. 1993.

5. Davies, A. G., Explosion hazards of au-toxidised solvents, J. Roy. InstituteChem. 1956, 80, 386–389.

6. Steere, N. V. (Ed.); Jackson, H. L.; Mc-Cormack, W. B.; et al., LXI—Control ofperoxidizable compounds, J. Chem. Ed.Safety Chem. Lab. 1970, 47(3), A175–188.

7. Peroxide forming chemicals, AppendixI, Prudent Practices for Disposal ofChemicals from Laboratories; NationalAcademy Press: Washington, DC, 1983.

8. National Research Council. PrudentPractices in the Laboratory: Handlingand Disposal of Chemicals; AcademicPress: Washington, DC, 1995.

16 Chemical Health & Safety, May/June 2000