Category → Safety resources
The University of California, San Diego, has a great new video on eye protection. It was produced by the chemistry department’s Haim Weizman, who was also the man behind A day in the lab, To be (safe) or not to be, Flash chromatography 101, and a trio of videos on working with pyrophoric reagents and reactive metals.
Overall, I think the “splash zone” video is a terrific illustration of why it’s important to always wear eye protection in labs, even when you’re not the one handling the chemicals. That said, the safety glasses featured in the video are really designed for impact protection, not splashes. For splash protection, people really need to use goggles.
Two letters in this week’s issue of C&EN follow up on the report from Alan R. Katritzky and Mirna El Khatib of an explosion in October, 2011, that resulted from acid workup of benzotriazole-1-sulfonyl azide:
We have two comments about the recent letter by Alan R. Katritzky and Mirna El Khatib concerning the organic azide workup explosion at the University of Florida, Gainesville (C&EN, Jan. 9, page 4). We commend the authors for pointing readers to the recent book “Organic Azides, Syntheses and Applications” by S. Bräse and K. Banert (John Wiley & Sons, 2009). The first chapter provides a good summary of hazard testing and evaluation, including an excellent list of general precautions and rules of thumb for azides and, by analogy, other energetic materials.
Dow Chemical has a reactive chemicals program that has been refined over the past 45 years and has been highly effective in reducing highly reactive chemical incidents. On the basis of our experience, we suggest additional resources and approaches for the hazard evaluation of reactive chemicals.
First, strategies for an overall reactive chemical hazard assessment based on scale and energy release potential have been described in “Selection of the Proper Calorimetric Test Strategy in Reactive Chemicals Hazard Evaluation” by David J. Frurip (Org. Process Res. Dev.,
Second, this event demonstrates the advantage of a “management of change” (MOC) policy, which assists successful and safe start-up of new procedures and chemistries. A MOC policy is a formal, structured process to evaluate any change (in this case, a workup in acid) by knowledgeable experts for its consequences. Completion of the MOC process is required before any new chemistries or procedures can be implemented.
This MOC policy is used currently with great success at Dow and by a large number of chemical companies worldwide. At the R&D scale, this MOC policy may sound burdensome, but the effort and review are scaled to address the perceived risk associated with the reviewed activity, and the policy is appropriately and efficiently applied. This sometimes consists of simply requiring a conversation with at least one independent and knowledgeable colleague.
By David J. Frurip and David B. Gorman / Reactive Chemicals
Jerry Klosin / Corporate R&D
Dow Chemical Co.
Katritzky and Khatib reported an explosion when handling benzotriazole-1-sulfonyl azide despite DSC data showing the compound to be thermally stable below 95 °C. However, when it comes to exploring potential hazards of azides, one needs to consider more than just its thermal stability on melting.
The properties of thermal stability, shock sensitivity, and explosivity are related, but not in a direct manner. For example, picric acid melts at 122 °C without decomposition but is shock-sensitive and explosive. Some compounds are shock-sensitive but not explosive, and others are explosive but only mildly shock-sensitive.
The DSC data given really say nothing about the potential of this azide to be either shock-sensitive or explosive. Most organic azides will thermally decompose, usually at temperatures below 200 °C. If the DSC experiment was carried out through the complete decomposition of the azide, the decomposition exotherm would in general yield the temperature at which decomposition is detected, the total energy released, and an estimate of the rate at which the energy is released.
Total decomposition energies above 1–2 kJ/g should be of greater concern. A broad decomposition exotherm in the DSC indicates that decomposition occurs slowly. However, a sharp exotherm indicates rapid decomposition and is indicative of explosive potential. A DSC experiment run to high enough temperatures to look for decomposition should be the first step in exploring potential hazards of any compound of unknown stability. Should high decomposition energies or rapid decomposition rates be found, or if the compound belongs to a class of materials like azides, diazo compounds, etc., that are known to be hazardous, then shock sensitivity should also be examined. This can be done with a standard drop-weight shock sensitivity test [ASTM E680-79(2011)e1], but the crude, old-fashioned hammer and anvil test can also be tried if the appropriate equipment or testing service is not readily available.
In this latter test, a small amount of sample (1–10 mg) is placed on an anvil and hit sharply with a hammer. If the sample is stable, it should appear unchanged. However, if the sample has darkened or charred, or if a loud report is heard beyond the normal bang of the hammer hitting the anvil, then the compound should be considered shock-sensitive. Shock sensitivity is a good indication that a compound might be explosive, but it is not proof.
Shock sensitivity simply means that a mechanical force can impart enough energy to a compound to make it decompose. The rate of decomposition is what is important. A good explosive is one with low shock sensitivity so it can be handled safely, but with high explosive power to do the intended job. Unless further testing is done, any compound showing shock sensitivity and high energy release should not be handled in other than milligram quantities except by someone who is an expert in the area of explosives.
All azides and diazo compounds should be handled as if they were shock-sensitive and explosive unless there are clear data to the contrary. When using sodium azide in a reaction, one should destroy any residual azide ion or hydrazoic acid with nitrous acid, followed by destroying any excess nitrous acid with urea during the workup so there is no hydrazoic acid or azide ion present when the product is isolated. When a particular azide structure is desired but found to be shock-sensitive, putting large inert substituents such as phenyl, phenoxy, or alkyl groups on the compound can result in a less sensitive material.
Hydrazoic acid is a water-soluble liquid that boils at 37 °C and can spontaneously explode when isolated. Whether hydrazoic acid or the acid workup has anything to do with the explosion, or whether the sulfonyl azide product in question is inherently shock-sensitive and explosive, is not clear from the information given. However, the properties of hydrazoic acid make it seem unlikely that the acid would end up mixed with the solid product in the bottom of a flask after an aqueous workup. Further testing of the benzotriazole-1-sulfonyl azide is required to definitively answer that question.
By Gary R. Buske
Responding to a request from several former ACS presidents, the ACS Division of Chemical Health & Safety is attempting to develop an online laboratory safety certification program aimed at chemistry graduate students. The program ideally would address longstanding complaints from industry that Ph.D. programs do not adequately educate students to work safely in industrial research and development laboratories. A well-planned and peer-reviewed online certification program could be part of the solution to this training gap.
The development cost for online training programs, according to an informal survey of commercial online training providers, is approximately $20,000 for each presentation hour of this type of safety course. This means that developing an 8- to 10-hour course with about a dozen training modules would cost $160,000 to $200,000.
The division is now facing the following questions and would welcome input from Safety Zone readers:
- How might costs be lowered? What work could be done by volunteers rather than paid consultants?
- Does ACS have the resources to develop the program without using a training provider?
- Several organizations are willing to support program development: the ACS Corporate Associates, National Academy of Sciences, National Research Council, and Council for Chemical Research. Are there others that might be interested?
- Is there sufficient demand to warrant developing the program? Can it meet industry’s needs?
- What topics should be covered, and what is a realistic amount of time to commit for effective training?
- Is taking an online course and passing tests sufficient for certification or should there be other components?
Related post: Teaching safety to chemical engineers
We have a safety letter regarding nitric oxide reactions in this week’s issue of C&EN:
Chemists at Merck & Co. were performing experiments using nitric oxide at high pressure (10–20 bar) when two instances of an explosion occurred during rapid depressurization of the NO headspace from a 500-mL closed reactor system. No injuries occurred, and damage was contained to the barricaded cell area. Both before and in between these events, NO had been used successfully about 100 times. Each explosion occurred after completion of the reaction, while venting through three-eighths- or one-quarter-inch i.d. Teflon-lined steel-braided tubing to atmospheric pressure.
Static electricity was suspected as the ignition source that, in conjunction with the presence of an oxidant (NO) and fuel (CH3OH), would lead to combustion. To confirm this hypothesis, an investigation was conducted. Preliminary results are communicated here.
The reaction system consisted of NO in conjunction with methanol under basic conditions. A literature search didn’t point to any existing cautionary notes about this reaction. Experimental ignition testing of NO systems was conducted by Fauske & Associates, which showed no combustion unless ignition energy greater than 3 J was used. This exceeds the energy typical of a static discharge, so it does not fully explain the observed combustion.
Further analysis of the reaction headspace using gas chromatography/mass spectrometry revealed that N2O was formed over time from a simple model system of NO + sodium methoxide + methanol. The conversion of NO to N2O and concomitant oxidation of methanol to formic acid proceeds to 50% in about six hours. Testing showed the energy needed to ignite the headspace of methanol under 1 bar of 50/50 NO/N2O is less than 3 mJ, several orders of magnitude lower than for similar systems without N2O.
On the basis of these results, the likely cause of the explosions is the combination of (a) formation of N2O gas and (b) generation of static potential caused by the rapid flow of gas and condensing methanol through the Teflon-lined tubing during rapid depressurization (while venting), which leads to sparking of sufficient energy to cause the combustible vapor to ignite.
We wanted to alert the chemical process industry to risks associated with this particular procedure. Anyone contemplating use of this chemistry should thoroughly evaluate its safety.
Daniel Muzzio, Ephraim Bassan, Erik Dienemann, Mark Weisel, Cameron Cowden, Scott Hoerrner, William Olsen, Michael Man-Chu Lo, Amjad Ali
We’ve got a safety letter in this week’s issue of C&EN:
We recently published details of a new diazo transfer reagent (benzotriazole-1-sulfonyl azide) (CAS Registry No. 1246367-30-5). We reported in our publication (J. Org. Chem., DOI: 10.1021/jo101296s) that differential scanning colorimetry of this compound shows that it is stable below 95 °C (melting point, 88 °C). Melting and resolidifying over two cycles of heating to 95 °C and cooling to −100 °C resulted in negligible material loss according to the heats of fusion and freezing.
Over more than a year we prepared this reagent on dozens of occasions and used it to convert amines into azides and a smaller number of active methylene compounds into diazo derivatives.
Until recently, we encountered no difficulty or untoward behavior in handling this compound. However, we recently found that when the experimental procedure was altered by mistake and an acidic workup (6N HCI) performed—followed by an attempt to remove the last traces of the solid using a metal spatula from a round-bottom flask—an explosion occurred, shattering the flask.
We still believe this compound can be used as an extremely effective diazo transfer reagent, but it requires very careful handling. In particular, the following safety measures are strongly recommended: All the safety precautions cited in the Journal of Organic Chemistry published work, particularly reference 7 (Bräse, S., and K. Banert. “Organic Azides, Syntheses and Applications,” 1st ed. West Sussex: John Wiley & Sons, 2009, 3–27), should be examined carefully for adequate protection, and the experimental procedure described in our JOC article for the synthesis of benzotriazole-1-sulfonyl azide should be strictly followed.
In particular, acidic workup should be avoided because of the possibility that trace amounts of residual sodium azide could be converted to highly explosive hydrazoic acid. It is possible that this was responsible for the explosion that occurred in this case.
By Alan R. Katritzky, Director Mirna El Khatib Florida Center for Heterocyclic Compounds
University of Florida Gainesville
‘Tis the season…for Organic Process Research & Development‘s annual “Safety Of Chemical Processes” section. The issue contains literature highlights, summarized as Safety Notables, as well as original papers.
First, though, comes an editorial by editor Trevor Laird, with a caution on including needed information in documents versus being overly comprehensive:
I recently reviewed a batch record for a simple process (add reagents, heat, monitor until complete, cool, quench, filter, and dry) and was surprised at the length of the document—over 300 pages. There was no doubt that the document was extremely comprehensive, but the question I ask is, Was it likely to be read by the process operator in the amount of detail that was provided? It was extremely complex, and I felt that any safety messages would have been lost in all the detail. In fact, with a document of such complexity I suspected that the operator would be more likely to make mistakes through having misunderstood what he was supposed to do. Surely these batch records can be simplified so that the operator’s instructions are clear. I must admit that I found it difficult to read the entire document and to find the information that I wanted.
Over at Endless Possibilities today, Katherine Haxton, a chemistry lecturer at the UK’s Keele University, discusses the safety talks that she’s giving to students at the start of the term. She asks:
Another thing that struck me as I was preparing the safety talks is how few undergrad lab safety talks there are available on the internet – do we all just hide them away in the dark recesses of our virtual learning environments? Are we scared to make them public just in case something happens that the talk didn’t cover? I would have thought that prospective students and their families, and those of current students might quite like the idea of being able to see the safety requirements set out somewhere. Just a thought. And where can we actually share best practice for undergraduate lab safety?
I know that the Journal of Chemical Education and the Journal of Chemical Health & Safety both publish papers related to lab safety education (and papers on some of the programs I wrote about last year appeared in JCHAS over the summer), but does anyone have ideas for faster, less formal dialogue in this area? If people have some good suggestions, perhaps this a project that the ACS Safety Culture Task Force would consider.
I spent much of my week following New Mexico’s Las Conchas wildfire, which caused the city of Los Alamos to evacuate and the adjacent Los Alamos National Laboratory to close. As of this morning, the fire is the largest known in New Mexico history, with more than 103,000 acres burned in a mere five days. Los Alamos and LANL generally appear to be out of danger at this point, but tribal lands to the north are sustaining heavy damage.
New Mexico is also battling two other significant fires: Donaldson, which has burned 73,000 acres since it started on Tuesday, and Pacheco, which has burned 10,000 acres over the last two weeks. Officials are clearly worried that other fires will be sparked by fireworks over the Fourth of July weekend. Governor Susana Martinez says that she does not have the authority to completely ban fireworks state-wide, but she ordered (pdf) state police to increase staffing to help enforce a state ban on fireworks in wildlands as well as any local restrictions. Walmart and grocery store chains Albertson’s and Smith’s have all pulled fireworks from store shelves in the state; Walmart and Albertson’s also evicted vendors from their parking lots.
Which brings me to say: If you plan to use fireworks this weekend, please be careful and don’t hurt yourself, your family, or your community. Perhaps consider watching a professional do it instead? (If you work with fireworks, OSHA has some information for you.)
Other chemical health and safety news from the past week:
- UCSD released a new safety video, this one aimed at undergrads
- Chembark considered the issue of working alone in lab
- More picric acid in Girl Scout first aid kits, in Colorado again and in Massachusetts
- More than half of the hazmat transportation incidents in Canada are due to human error: “Improperly loading, unloading and handling dangerous cargo, drivers losing control of their vehicles, and carelessness and negligence.”
- A wall of a chemistry building collapsed at Sindhu College in India. “Principal B Nag said it was just an accident and college authorities were not responsible for it. ‘The chemistry lab building is old and since the water tank is on the same floor, the place was moist and hence the wall collapsed partly,’ he said.” So it’s not the school’s responsibility to maintain facilities so that walls don’t fall down?
Fires and explosions:
- A lightning strike apparently caused a fire in a hydrochloric acid tank at SiVance in Florida
- A magnesium fire at Olympic Tool & Machine In Pennsylvania injured four, one with severe burns
- A fire at a pesticide-manufacturing factory in India also damaged neighboring buildings
Leaks, spills, and other exposures:
- Chlorine gas was released at a Tyson Foods plant in Arkansas after a chlorine solution was accidentally added to a drum of acid; 300 workers were evacuated, 173 treated for exposure, and at least 45 were admitted to the hospital (two were still hospitalized three days later)
- And more chlorine was released from a leaking canister at an Airgas facility in Florida
- A Notre Dame stduent was splashed in the eye with something–why was he not wearing eye protection?
- On roads, railways, and shipards: an acid used in lotions, fertilizer, liquid asphalt, coal tar oil, sodium hypochlorite, more sodium hypochlorite
Not covered: meth labs; ammonia leaks; incidents involving floor sealants, cleaning solutions, or pool chemicals; and fires from oil, natural gas, or other fuels
Map from InciWeb.