Corrosives, oxidizers, reactives and peroxide formers

Flammable liquids get most of the attention in fire codes, but many serious chemical storage incidents involve other groups: corrosives that eat through containers and shelving, oxidizers that turn ordinary combustibles into fierce fires, reactive chemicals that decompose or explode, and peroxide-forming chemicals that become shock-sensitive as they age. This lesson covers how to store each of these groups safely. The chemistry behind them is covered in CHEM-101 and CHEM-102; here the focus is on containers, locations, inspection and time limits.

Corrosives

Corrosives are acids and bases that damage skin, eyes and metals. In storage, their main hazards are container failure, fumes that corrode shelving, cabinets and nearby equipment, and violent reactions with incompatible chemicals. Common workplace corrosives include sulfuric acid (battery acid, drain openers), hydrochloric acid (muriatic acid, concrete etch), phosphoric acid (rust removers), sodium hydroxide (caustic soda, oven and drain cleaners), potassium hydroxide, and ammonia solutions.

Store corrosives in their original containers or in containers made of a compatible material. Most acids and bases are stored in polyethylene; hydrofluoric acid must never be stored in glass because it dissolves silica. Keep them in corrosion-resistant cabinets or on low shelves in trays, with acids separated from bases. Keep oxidizing acids (nitric, perchloric, chromic) apart from organic acids and from all organics. Inspect containers regularly for bulging, cracking, crystal build-up around caps, and discoloured labels, which are signs of slow leaks or fumes.

Oxidizers

Oxidizers supply oxygen or accept electrons, so they make other materials burn more intensely and can start fires on their own when they contact combustibles. They are not usually flammable themselves, which leads people to underestimate them. Common workplace oxidizers include hydrogen peroxide solutions, calcium and sodium hypochlorite, nitrates (ammonium nitrate, potassium nitrate), chlorates and perchlorates, permanganates, dichromates, and pool shock products.

Store oxidizers in a cool, dry place away from flammables, combustibles, reducing agents, organic materials and anything that might fuel a fire. That includes wooden shelves, cardboard boxes, paper, oily rags and sawdust. Oxidizer spills absorbed with sawdust or paper towels can ignite. Use inert absorbents such as sand or vermiculite listed on the SDS. Keep large quantities of oxidizers, especially solid ones such as ammonium nitrate and calcium hypochlorite, in dedicated areas and limit the amount on hand.

Fire codes classify oxidizers by how strongly they promote combustion, using classes 1 to 4 in NFPA 400 and the fire codes based on it, and by GHS categories 1 to 3 for oxidizing solids and liquids in hazard communication. Higher classes have tighter quantity limits and stricter separation requirements. The 2020 port explosion in Beirut, where about 2,750 metric tons of ammonium nitrate stored for years in a warehouse alongside other goods detonated after a fire, and the 2015 Tianjin port explosions, which killed 173 people, are extreme reminders of what happens when large quantities of oxidizers and reactive chemicals are stored without proper segregation and control.

Reactive and unstable chemicals

Reactive chemicals are those that can undergo violent reactions on their own or with common triggers. The GHS covers several such hazard classes: self-reactive substances, organic peroxides, pyrophoric liquids and solids that ignite in air, self-heating substances, substances that release flammable gas in contact with water, and explosives. In workplaces outside chemical manufacturing, the most common reactives are organic peroxides (resin hardeners), water-reactive metals (sodium, potassium, lithium), metal hydrides, calcium carbide, and pyrophoric reagents in research laboratories.

Storage rules for reactives are strict and product-specific. Keep quantities to the minimum. Follow the temperature range in SDS section 7; some organic peroxides must be kept refrigerated in a spark-free refrigerator. Keep water-reactive and pyrophoric materials in sealed containers under inert gas or oil as supplied, away from water sources and sprinklers where possible, and inform the fire department. Store them in a dedicated cabinet with a sign. Never return unused material to the original container, because contamination can trigger decomposition.

The 2008 death of Sheri Sangji, a research assistant at the University of California, Los Angeles, followed a fire when the pyrophoric reagent tert-butyllithium ignited as she transferred it with a syringe. She was not wearing a lab coat. The case led to criminal charges and to major changes in laboratory safety programs in the United States, and it shows that the transfer of reactive materials is as important as their storage. Transfers are covered in lesson 9 and laboratory practices in lesson 11.

Peroxide-forming chemicals

Some common solvents and reagents react slowly with oxygen in air to form organic peroxides, which can accumulate as crystals around the cap or in the liquid, especially if the solvent evaporates or is distilled. These peroxides can explode when the container is opened, shaken or heated. The classic examples are diethyl ether, tetrahydrofuran (THF), 1,4-dioxane and isopropyl ether. Peroxide formation is speeded by light, heat, air in the headspace and the removal of inhibitors.

Good practice for peroxide formers is to buy small containers, date them when received and when opened, store them in the dark in tightly closed containers, keep inhibitors in place, test for peroxides at set intervals with test strips, and dispose of containers before they reach their time limit. A container that is past its date, has visible crystals around the cap, or has an unknown history should not be opened or moved. Leave it in place, keep people away and call a specialist hazardous waste contractor or the local bomb disposal unit, as advised by your safety office.

# Flag peroxide formers that are due for testing or disposal.
from datetime import date
today = date(2026, 10, 19)
limits_days = {"A": 90, "B": 365, "C": 180}   # guideline days after opening
stock = [
    ("diethyl ether 1 L",   "B", date(2025, 9, 3)),
    ("THF 4 L",             "B", date(2026, 6, 1)),
    ("isopropyl ether 500 mL", "A", date(2026, 6, 20)),
    ("styrene 1 L",         "C", date(2026, 2, 1)),
]
for name, grp, opened in stock:
    age = (today - opened).days
    due = limits_days[grp]
    status = "OVERDUE - do not open; arrange disposal" if age > due else f"ok, {due - age} days left"
    print(f"{name:24s} group {grp}  opened {age:3d} days  {status}")

diethyl ether 1 L        group B  opened 411 days  OVERDUE - do not open; arrange disposal
THF 4 L                  group B  opened 140 days  ok, 225 days left
isopropyl ether 500 mL   group A  opened 121 days  OVERDUE - do not open; arrange disposal
styrene 1 L              group C  opened 260 days  OVERDUE - do not open; arrange disposal

The check flags the ether, which is more than a year past opening, and the isopropyl ether, a group A former that is past three months. Both need specialist assessment rather than routine handling. Building this check into an inventory system with opening dates is one of the simplest ways to prevent peroxide incidents.

Other groups needing special attention

Toxic and very toxic chemicals, including cyanides, arsenic compounds, mercury and its compounds, and some pesticides, need locked storage with limited access and careful inventory, both to protect workers and to prevent theft. Carcinogens, mutagens and reproductive toxicants should be in clearly labelled areas with designated handling procedures. Some chemicals are also controlled for security reasons; in the United States, the Chemical Facility Anti-Terrorism Standards (CFATS) program lapsed in July 2023 when Congress did not reauthorize it; bills to restore it have been introduced since, so facilities should check the current status with the Cybersecurity and Infrastructure Security Agency (CISA) (checked October 2026). In Canada, explosives precursors and some chemicals are regulated under the Explosives Act and its regulations. Keep security-sensitive materials locked and reconcile their inventory.

Quantity, time and temperature

Three variables decide how dangerous most reactive and special-group chemicals become in storage: how much is present, how long it has been there, and how warm it gets. Reducing any of them reduces the hazard. Quantity is controlled by purchasing small containers and limiting stock to what is needed for a few months. Time is controlled by dating containers on receipt and opening and by disposing of them before their recommended limits, as shown for peroxide formers. Temperature is controlled by storing away from heat sources and sunlight and, for some products such as organic peroxides, in temperature-controlled storage with an alarm.