GHS / HazCom term · Glossary
Self-Heating Substance
Verified vs OSHA sources · 2026-10-05
A solid or liquid chemical — other than a pyrophoric — that reacts with air and, without any energy supply, is liable to self-heat. Unlike a pyrophoric (which ignites within minutes), a self-heating substance ignites only when present in large amounts (kilograms) and after long periods (hours or days), once the rate of internally generated heat outpaces the rate it can escape. GHS assigns Category 1 or 2, with the GHS02 flame pictogram.
Also known as: self-heating chemical
Self-Heating Substance at a glance
- Self-heats by reaction with air, with no external energy input.
- Ignites only in large amounts (kilograms) and after long periods (hours or days).
- Distinguished from pyrophorics, which ignite fast (≤5 min) and even in small quantities.
- Two GHS categories (1 and 2); GHS02 flame pictogram.
In plain English
A material that slowly warms itself up by reacting with air. In a big enough pile, and given enough time, that heat builds until it catches fire on its own — think a large heap of oily rags or damp organic material igniting hours later.
What the source says, in summary
A self-heating chemical is a solid or liquid chemical, other than a pyrophoric liquid or solid, which, by reaction with air and without energy supply, is liable to self-heat; this chemical differs from a pyrophoric ... in that it will ignite only when in large amounts (kilograms) and after long periods of time (hours or days).
In context
A classification or labeling concept from the UN Globally Harmonized System, adopted into US law through OSHA's Hazard Communication Standard (29 CFR 1910.1200) and its appendices.
Where this is written in OSHA's rules
- 29 CFR 1910.1200 App B.11Read on eCFR / OSHA.gov
Example
A large bin of rags soaked in linseed oil can undergo self-heating: oxidation warms the pile, the heat can't escape the center, and hours later it reaches ignition and combusts spontaneously. The same oil on a single rag in open air won't — the mass and insulation are what make it dangerous.
Why it matters
Self-heating causes “spontaneous combustion” fires in warehouses, laundries, and bulk storage that seem to start from nothing, often long after the material was set down. Because the hazard scales with quantity and time, controls focus on pile size, ventilation, and not stockpiling — details the GHS classification exists to flag.
Self-heating vs. pyrophoric
Same underlying mechanism (reaction with air, no ignition source), opposite tempo. A pyrophoric ignites within 5 minutes, even in tiny amounts. A self-heating substance ignites only in bulk (kilograms) and slowly (hours/days). If it flares immediately, it's pyrophoric; if a big pile smolders to ignition overnight, it's self-heating.
Self-heating substance vs. pyrophoric
| Attribute | Self-heating | Pyrophoric |
|---|---|---|
| Time to ignite | Hours to days | Within 5 minutes |
| Amount needed | Large (kilograms) | Even small quantities |
| Typical example | Bulk oily rags, damp organics | Alkyllithium, white phosphorus |
Self-Heating Substance: frequently asked questions
- What is a self-heating substance?
- A solid or liquid (other than a pyrophoric) that reacts with air and self-heats without any energy supply. In large amounts and over long periods, that self-heating can lead to spontaneous ignition.
- How is it different from a pyrophoric substance?
- A pyrophoric ignites within five minutes, even in small quantities. A self-heating substance ignites only in large amounts (kilograms) and after hours or days — slow and bulk-dependent rather than fast.
- Is spontaneous combustion of oily rags an example?
- Yes. A large mass of oil-soaked rags can self-heat through oxidation until it ignites hours later — a classic self-heating (spontaneous combustion) scenario driven by quantity and trapped heat.
Related terms
Free tools for this
Governing OSHA standards
More GHS terms
A GHS health-hazard class for the harmful effects that follow a single dose, several doses within 24 hours, or a 4-hour inhalation exposure. Chemicals are sorted into categories by route (oral, dermal, inhalation) using LD50/LC50 cut-offs — Category 1 is the most toxic. OSHA's HazCom standard uses Categories 1–4.
Aspiration HazardA GHS health-hazard class for chemicals that can be fatal if swallowed and then enter the airways — directly or by vomiting — causing chemical pneumonia or lung injury. Thin, low-viscosity hydrocarbons (gasoline, kerosene, lamp oil) are the classic example. It is Category 1, with the health-hazard pictogram (GHS08) and signal word “Danger.”
CarcinogenicityA GHS health-hazard class for chemicals that cause cancer or increase its incidence. GHS (and OSHA's HazCom standard) sorts carcinogens into Category 1A (known human carcinogen), 1B (presumed, from animal evidence), and Category 2 (suspected). Carcinogens carry the health-hazard pictogram (GHS08) and a hazard statement such as H350 (“May cause cancer”).
Chemicals Under PressureA physical-hazard class added by OSHA's 2024 HCS update (aligning with GHS Revision 7) for liquids or solids pressurized with a gas, held in pressure receptacles other than aerosol dispensers and not classified as gases under pressure. It is categorized by the flammability of its contents and always carries the gas-cylinder pictogram (GHS04) for the pressure hazard.
ClassificationThe process of evaluating the available scientific evidence for a chemical against the GHS criteria to decide whether it is hazardous and, if so, the hazard class and category of each effect. Classification is the first step in HazCom — its result determines every label element (pictogram, signal word, hazard and precautionary statements) and SDS content.
Corrosive to MetalsA GHS physical-hazard class for chemicals that, by chemical action, will materially damage or even destroy metals. It is a single category (Category 1), determined by corrosion-rate testing on steel and aluminum, and uses the corrosion pictogram (GHS05) with the hazard statement H290. It is a separate hazard from skin corrosion, even though both use GHS05.
Desensitized ExplosivesA physical-hazard class added by OSHA's 2024 HCS update (GHS Revision 7) for solid or liquid explosives that have been phlegmatized — wetted or diluted — to suppress their explosive properties for safe transport and storage. It has four categories based on the corrected burning rate, and uses the flame pictogram (GHS02), not the exploding-bomb.
Globally Harmonized System (GHS)An internationally agreed framework created by the United Nations (first adopted in 2003) that standardizes how chemical hazards are classified and communicated — using common hazard classes, pictograms, signal words (Danger / Warning), and coded hazard (H) and precautionary (P) statements on labels and safety data sheets. The US adopted GHS into law through OSHA's 2012 Hazard Communication Standard update.
Sources & verification
- 29 CFR 1910.1200 App B.11 (eCFR / OSHA.gov)
- OSHA — 1910.1200 Appendix B.11 (Self-Heating Chemicals)
- OSHA — Hazard Communication (Physical Hazards)
Reviewed by HazComFast against eCFR, OSHA.gov, NIOSH, and the Federal Register. Last reviewed 2026-10-05. This glossary is general information, not legal advice; OSHA State-Plan states (e.g. California, Michigan) may adopt stricter requirements.
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