Time-Sensitive Chemicals Guide
This guide describes methods for safely storing, using, and disposing of time-sensitive chemicals, i.e., any chemicals or chemical products that develop additional hazards upon prolonged storage.
Time-sensitive chemicals may include:
- Peroxide Formers: Oxygenated organic compounds react with atmospheric oxygen to form explosive peroxides. Examples commonly found in our labs include sodium amide, diethyl ether, dioxane, THF, and benzyl alcohol.
- Polynitrated Aromatics: Compounds with reactive nitrate groups can form explosive picrate salts when exposed to certain metals. Examples include dinitrotoluene, dinitrophenol, hexanitrostilbene, and nitroglycerin.
- Shock-Sensitive Chemicals: Any chemical that could detonate due to heat, friction, and/or shock. Examples include picric acid, hydrazine, ammonium nitrate, and perchloric acid.
- Chloroform: Reacts with air over time to form phosgene – a deadly, odourless gas.
- Anhydrous HF: Easily liquefies and can react with a carbon steel container in the presence of moisture to form hydrogen and iron fluoride. This can cause an increase in cylinder pressure due to the hydrogen gas buildup over time.
Hazard Identification Methods
With any time-sensitive chemical, the date received, and the date opened should be written on the container. In addition, the following visual cues can alert you that hazardous conditions have formed inside the container:
- Peroxide Formers may be characterized by having a mossy look around the cap. In addition, there may be a white film or residue around the container's neck, threads or lid, or there may be crystals in the liquid. For solid peroxide formers, there may be discolouration or the formation of a surface crust.
- Polynitrated Aromatics which have dehydrated will be pale in colour, and crystals may be present.
- Chloroform will have a normal appearance. The only way to determine stability is by the age of the material.
- Anhydrous HF cylinders may show a buildup of pressure in the cylinder's regulator.
Peroxide Formers
Safe Storage Periods for Peroxide Formers
Unopened containers | 12 months |
Opened containers, dispose or test after:
Chemicals in Table A | 3 months |
Chemicals in Tables B and D | 12 months |
Uninhibited chemicals in Table C | 24 hours |
Inhibited chemicals in Table C (Do not store under an inert atmosphere) | 12 months |
Time-Sensitive Chemicals Table
Peroxidizable Organic Moieties
Peroxide test strips are available commercially, which turn to an indicative colour in the presence of peroxides. These strips must be air-dried until the solvent evaporates and then exposed to moisture for proper operation. This gives a quantitative peroxide concentration, usually in parts per million (ppm). Anything > 50 ppm should not be handled. The Departmental Technical Staff and/or Health & Safety Officer should be notified immediately.
Caution: these strips have specific measurement ranges. Read the product information or call the manufacturer for more info.
Make sure you purchase material that contains an appropriate peroxide inhibitor or stabilizer, such as butylated hydroxytoluene (BHT) or ethanol. If you must store non-inhibited material, be sure to store the material under an inert atmosphere of nitrogen or argon and test it for peroxides at least once a month.
Do not distil, evaporate or concentrate the material until you have first tested the material for the presence of peroxides. Peroxides are usually less volatile than their parent material and tend to concentrate in the (hot) distillation pot. Do not use a metal spatula when working with any peroxide formers.
NOTE: Never, under any circumstances, touch or attempt to open a container of peroxide-forming liquid if there are whitish crystals around the cap and/or in the bottle. The friction of unscrewing the cap could detonate the bottle and cause severe injury.
Polynitrated Aromatics
Picric acid and its derivatives should be stored in small quantities, within the original container and in a cool, dry, well-ventilated area that is away from heat sources. Picric acid is considered a flammable solid and is incompatible with oxidizers, reducing agents, inorganic salts, metals, alkaloids .Improperly managed or stored picric acid may become sensitive to shock, friction, and heat. Picric acid allowed to dry out to less than 10% water by volume, becomes unstable and may pose an explosion hazard in your laboratory. If the material appears dry, do not open or handle the container – immediately contact the Departmental Technical Saff and/or Health & Safety Officer.
Picric acid should be monitored for water content every three months. The material should look like a wet paste. Dispose of unused picric acid as hazardous waste within two years of receipt. Do not use a metal spatula when working with any polynitrated aromatics.
Shock-Sensitive Chemicals
Materials listed as shock sensitive or explosive should not be stored for prolonged periods. They should be kept away from reducing agents, flammable and combustible materials, and away from dehydrating agents. Shock-sensitive materials should be stored in a cool, dry area and protected from heat, shock, and friction.
Chloroform
Chloroform should be stored in a cool, dry, well-ventilated area (< 30 ˚C) and in tightly sealed containers. This is because chloroform decomposes at normal temperatures in sunlight in the absence of air and in the dark in the presence of air.
Phosgene is a decomposition product of chloroform. Phosgene exposure can cause damage to the central nervous system and can be fatal.
If possible, chloroform that is stabilized with alcohol should be purchased. If non-stabilized chloroform is necessary for the work, it must be treated like peroxide-forming compounds and used or disposed of quickly. Amylene is also a stabilizer, but there is evidence that it may not prevent phosgene generation.
If you find unstabilized chloroform older than one year, it should be immediately disposed of as hazardous waste.
Stabilized chloroform should be disposed of after it has been open for over one year.
Compressed Gas Cylinders
Compressed gases such as hydrogen fluoride, hydrogen bromide, hydrogen sulfide, hydrogen cyanide, and hydrogen chloride (all anhydrous forms) have a short shelf-life provided by the manufacturer, which must be strictly adhered to. Gases such as hydrogen fluoride and bromide may react with the metal walls of the cylinders to produce hydrogen. The gaseous hydrogen collects in the vapour space and builds pressure over an extended period.
To minimize the possibility that the pressure would build to unsafe levels, cylinders should be pressure checked with a suitable pressure gauge during the manufacturer's recommended maximum shelf life period (usually 2 years or less). Cylinders should be returned to the supplier after that time or if they are not being used.
Corrosive gases can also increase hazards over time. Corrosives can damage valves, so they cannot be fully opened or closed. Valves on corrosive gases should be closed when not in use.
A First In First Out (FIFO) inventory rotation should be applied to any cylinders used in your laboratory. The potential exists for pressure increases of several hundred pounds during the recommended storage time frame of Anhydrous HF. In addition, pressures may continue to rise over more extended storage periods. If you discover any HF cylinders that have been in storage longer than two years, immediately contact the Departmental Technical Saff and/or Health & Safety Officer.
Management of Time-Sensitive Chemicals
Laboratory personnel should be mindful of their time-sensitive chemicals, and request pickups for any expired or not needed material. In addition, it is recommended to only order as many of these chemicals as will be reasonably used by their expiration dates.
To assist the laboratory personnel with managing their time-sensitive chemicals, the department does checks Chemical inventory and will contact laboratories with material with a date older than the recommended safe storage time.
Waste Disposal
If you need to request a waste pickup for your time-sensitive materials, please visit Schedule for Booking Waste Collection (supersaas.co.uk) and follow the link to the Waste Pickup Form.
Adapted from: https://www.baylor.edu/ehs/index.php?id=97719