What temperature should the store be held at?

There is no single number, because the requirement is relative rather than absolute: the liquid must stay comfortably below the flash point given in section 9 of the safety data sheet for the grade you hold, and it must stay out of direct sun and away from radiant heat sources. A flammable liquid of this category has a flash point above normal room temperature but within the range a steel drum standing on a sunlit yard can reach on a hot day. Shade, ventilation and a temperature that does not track the weather do more than any specific set point.

Does this solvent really form peroxides, and how would we know?

Ether linkages autoxidise slowly in contact with air, and glycol ethers are recognised as capable of forming unstable peroxides on storage. The risk in normal use is low because the peroxide stays dilute; it becomes serious when the solvent is distilled or evaporated, because peroxides are far less volatile than the solvent and concentrate in the residue. The control is procedural: date every container on receipt, set a retest interval, test with peroxide indicator strips before any distillation, and never evaporate a batch to dryness.

Can we store drums outdoors if the store is full?

It is the arrangement that produces most water contamination. A drum left in the open breathes as it warms and cools, and rain standing in the dished head is drawn past the bung as the drum cools at night. If outdoor storage cannot be avoided, keep drums on their side with both bungs at the horizontal centre line, or tilted so water runs off the head, and use covers. Then treat every such drum as requiring a water test before use rather than assuming the certificate still applies.

Which container and gasket materials are safe?

For bulk, stainless steel is the usual choice and carbon steel is workable where colour is not critical, provided the tank is clean and not rusty, since iron and other transition metals accelerate oxidation. Copper and copper alloys are best avoided in wetted service for the same reason. For gaskets, seals and diaphragms, confirm compatibility against this specific solvent with the equipment supplier rather than assuming, because glycol ethers swell or extract a number of common elastomers; fluoropolymer seals are the usual safe default.

What do we do with empty drums?

Treat them as full of vapour, because that is what they are. A drained drum holds a flammable vapour and air mixture and has caused more injuries than full ones. It must never be cut, drilled, welded or heated, it must keep its original hazard label until it has been properly cleaned, and it should be stored bunged in the same segregated area as full stock until collection. Dispose of it through a licensed contractor against the waste code in section 13 of the safety data sheet.

Storing propylene glycol ethyl ether without incident

Technical article · Eapearl Chemical · 17 June 2026

Storage incidents with this solvent are not exotic. Almost all of them trace back to one of four things: an ignition source reaching vapour, a static discharge during transfer, peroxide concentrated by evaporation, or water finding its way into a drum that was left outside. Each has a specific engineering answer, and none of them is solved by a sign on the door.

Know exactly which material you are storing

Propylene glycol ethyl ether is supplied as a mixture dominated by the secondary-alcohol isomer, 1-ethoxy-2-propanol, CAS 1569-02-4; the isomer mixture is also traded and registered under CAS 52125-53-8. The molecular formula is C₅H₁₂O₂ and the molar mass 104.15. It is a clear, water-miscible liquid with both an ether linkage and a hydroxyl group, and both of those structural features matter for storage, as the sections below explain.

Its harmonised classification under the CLP Regulation is signal word Warning with H226, flammable liquid and vapour, and H336, may cause drowsiness or dizziness. A harmonised entry is a legal minimum that no supplier may classify below. Everything else about the grade in your tank, including flash point, boiling range and any national occupational exposure limit, comes from the safety data sheet for that grade, which is the document the store should be designed around.

Two properties that are not in the classification but govern the layout of the store: the vapour is heavier than air, so it collects at low level, in pits, sumps and bunds; and the liquid is fully miscible with water, so a spill will not float and can be separated out of a drain system only with difficulty.

Fire and ignition

What the category means in practice

H226 places this material in the flammable liquid category whose flash point sits above ordinary room temperature but still below the upper limit that separates it from the non-flammable classes. That is a genuinely awkward band. It is high enough that the liquid seems unremarkable in a cool warehouse, and low enough that a drum in direct summer sun, a container next to a steam line or a tank in an unshaded yard can reach flash point without anything unusual happening. Design for the worst temperature the package will actually see, not the temperature of the store on the day of the survey.

The store itself

A dedicated, fire-rated flammable liquids store or cabinet, sized to the inventory you actually hold, with the maximum quantity written down and enforced rather than implied.
Ventilation at low level as well as high, because the vapour sinks. High-level extraction alone leaves the hazard exactly where people stand.
Bunding to retain the largest single container plus a margin, with no drain connection from the bund to a surface water system.
Ignition source control across the whole hazardous area: electrical equipment rated for the zone, no hot work without a permit that names this store, no smoking, no space heaters with exposed elements, and mechanical handling equipment rated for the area.
Segregation from strong oxidising agents, strong acids and strong bases, and from anything on the incompatibility list in section 10 of the safety data sheet.

Static electricity

This is the ignition source most often left out of a storage assessment, because it is generated by the operation rather than present in the room. A low-conductivity organic liquid accumulates charge as it flows through pipework, through a filter or through a filling nozzle, and the charge separates again as the liquid splashes into a receiving container. The discharge that follows can find a flammable headspace at exactly the moment the headspace exists.

The controls are well established and cheap:

Bond and earth the delivery container and the receiving container to each other and to a verified earth point before the closure is opened, not after flow has started.
Fill by dip pipe or submerged fill to avoid free fall and splash filling into the headspace.
Control flow velocity during pumping, and pay particular attention immediately downstream of filters, which are efficient charge generators.
Use conductive or dissipative containers and funnels. Decanting into a plain plastic pail removes the earth path entirely and is a common informal practice worth designing out.
Allow a relaxation time after filling before gauging or sampling, and use bonded sampling equipment.

Peroxides: the slow hazard

The ether oxygen in this molecule makes it susceptible to slow autoxidation in contact with air, forming peroxides. Under normal warehouse conditions the concentration stays low and the material is entirely routine to handle. The hazard appears when the solvent is concentrated, because peroxides are much less volatile than the solvent itself: distillation, solvent recovery or evaporation leaves them behind in the residue, where they can reach an energetic concentration in the last few percent of a batch.

Storage practice therefore has to be designed for a hazard that is invisible on the day the drum arrives.

Exclude air. Keep containers closed, keep bulk tanks under a nitrogen blanket, and avoid leaving part-used drums open or half-empty for long periods.
Exclude light and heat. Store cool and out of direct sunlight; both accelerate the reaction.
Exclude catalysts. Rust, copper alloys and other transition metal surfaces in wetted service accelerate oxidation. Tank and line material selection is part of the peroxide control, not a separate topic.
Date every container on receipt and operate strict first-in, first-out rotation with a defined retest interval. Undated stock is the root cause in most peroxide incidents.
Test before concentrating. Peroxide indicator strips before any distillation or evaporation, and an absolute rule that no batch is taken to dryness.

Water, colour and the quality side of storage

Because the liquid is fully water-miscible, it takes up atmospheric moisture readily and gives no visual warning when it does; there is no cloud point to see and no separate layer to drain. Water then shows up as a failed coating, a shifted evaporation profile or an off-specification Karl Fischer result at the customer.

The classic entry route is a drum stored outdoors. As the drum warms and cools it breathes, and rain standing in the dished head is drawn past the bung seal on the cooling cycle. Bulk tanks have the same problem through the vent, which is why a desiccant breather is standard on any tank holding a hygroscopic solvent.

Practical measures: store indoors wherever possible; if drums must stand outside, lay them on their side with both bungs at the horizontal centre line, or tilt them so water runs clear of the head, and cover them. Keep bungs fully tightened between uses. Fit and maintain a desiccant breather on bulk storage. Recheck water content, colour and acidity on any container whose retest date has passed or whose storage history is uncertain.

Procedures, documentation and the human layer

Labelling. Every decanted container carries the full hazard label, including the H statements, not a hand-written abbreviation. Unlabelled decants are how the wrong solvent reaches the wrong process.
Inventory. Record what is held against the licensed or assessed maximum, and reconcile it. A store that has quietly doubled its inventory has invalidated its own fire assessment.
Safety data sheets available at the store in the language of the people working there, with the current version.
Spill response. Non-sparking tools, a non-combustible absorbent in place and in date, drains protected before a transfer begins rather than after a spill. Because the solvent is water-miscible, washing a spill down is the worst available option.
Exposure control. H336 means narcotic effects, so transfers and open handling need local extraction and the exposure limit from section 8 of the safety data sheet applied, not assumed.
Receipt and transport. Check the label and the certificate against the order at goods-in, including the CAS number, and take the transport classification, UN number and packing group from section 14 of the safety data sheet rather than from a general reference.
Empty containers. Kept bunged, kept labelled, never cut or heated, and consigned to a licensed waste contractor.

A short storage audit

Walk the store and answer these seven questions honestly. Every negative answer is a specific, cheap corrective action rather than a project.

Is every container dated on receipt, and is stock rotated on those dates?
Is there a verified earth point and a bonding cable at every place where liquid is transferred?
Does the ventilation remove vapour from low level?
Can any drum in this inventory reach direct sunlight or a heat source?
Does the bund drain anywhere?
Does anyone distil or recover this solvent, and if so where is the peroxide test record?
Is every decanted container fully labelled right now, not in principle?

Related grades in this family are listed under glycol ethers, including propylene glycol monomethyl ether. For grade selection, a specimen certificate of analysis or the safety data sheet in a specific language, use contact and state the receiving site.