n-Heptane (CAS 142-82-5) is one of the most widely traded aliphatic hydrocarbon solvents in the chemical trade, and the question of whether it is toxic to humans comes up every time it is specified for extraction, laboratory work, or precision cleaning. This guide summarises what the hazard data actually show, which national exposure limits apply, and how the material should be stored, dosed, and handled in a manufacturing environment.
What Is n-Heptane?
n-Heptane is a straight-chain saturated hydrocarbon with the molecular formula C7H16. It is a colourless, volatile liquid with a faint petroleum odour. The molecule is nonpolar, so it is practically insoluble in water but readily soluble in ethanol, diethyl ether, chloroform, and other organic solvents. Its best-known role is as the zero point of the octane number scale: by definition n-heptane is rated 0 and isooctane is rated 100, and gasoline knock resistance is measured against that pair.
| CAS number | 142-82-5 |
| Molecular formula | C7H16 |
| Molar mass | 100.2 g/mol |
| Appearance | Colourless volatile liquid |
| Boiling point | 98.4 °C |
| Melting point | -90.6 °C |
| Flash point | -4 °C closed cup |
| Density at 20 °C | 0.684 g/cm3 |
| Vapour pressure at 20 °C | about 4.6 kPa |
| Water solubility | Practically insoluble |
| UN number | 1206, flammable liquid |
Is n-Heptane Toxic to Humans?
The short answer is that n-heptane is not a highly toxic substance at short-term, low-level exposure, but it is certainly not a benign one. Under the GHS classification the liquid is not assigned an acute oral, dermal, or inhalation toxicity category, which reflects its low acute toxicity profile. What does drive the classification is flammability together with three specific hazards: narcotic effects on the central nervous system at high vapour concentrations, irritation of skin and mucous membranes, and an aspiration hazard if the liquid enters the lungs.
In practice the fire and explosion hazard usually overtakes the toxicological hazard in a plant risk assessment, because the very properties that make n-heptane an excellent solvent - low viscosity, high volatility, and a low flash point - also allow it to generate flammable vapour at ambient temperature. The toxicological risk is controlled by ventilation and exposure limits rather than by flammability engineering.
Health Effects by Route of Exposure
Inhalation: Vapours irritate the nose, throat, and airways, producing coughing, sore throat, and shortness of breath. Higher concentrations act as a central nervous system depressant, causing headache, dizziness, euphoria, drowsiness, and loss of coordination. Very high concentrations in poorly ventilated or confined spaces have caused loss of consciousness.
Skin contact: Repeated exposure defats the skin, leading to dryness, cracking, redness, and a form of contact dermatitis. Prolonged or widespread skin contact with the liquid should be avoided because it also increases the chance of systemic uptake.
Eye contact: Splashes cause stinging, tearing, and transient conjunctival redness. The effect is usually reversible but should be flushed with water for at least 15 minutes.
Ingestion: Swallowing irritates the gastrointestinal tract and may produce nausea, vomiting, and abdominal pain. The far more serious risk is aspiration: if the liquid or vomit is inhaled into the lungs it can cause chemical pneumonitis, so vomiting should never be induced.
Repeated high-level exposure: Workers exposed repeatedly to elevated solvent vapour concentrations have shown reversible effects on the central nervous system such as fatigue, sleep disturbance, and reduced concentration. Good occupational hygiene keeps exposure well below the limits given below, and this is where the practical control effort belongs.
Fire, Explosion and Reactivity Hazards
n-Heptane is a class 3 flammable liquid. Its vapour is heavier than air and can travel along floors and pits to a distant ignition source before flashing back. Vapour mixed with air forms explosive mixtures over a wide range, typically from about 1.0 to 6.7 percent by volume, so the absence of an ignition source at the point of use is not sufficient protection on its own. Static discharge during transfer, hot work in adjacent areas, and non-rated electrical equipment are the most common ignition routes in storage and blending areas.
The material is stable under normal storage conditions, but it reacts vigorously with strong oxidisers such as concentrated nitric acid, peroxides, and chlorates. Storage must therefore segregate n-heptane from oxidising agents, and all transfer equipment must be bonded and grounded.
Workplace Exposure Limits and Control Measures
The main engineering controls are local exhaust ventilation at the point of vapour generation, closed transfer systems, and continuous or periodic monitoring where the material is handled in bulk. Where ventilation alone cannot hold concentrations well below the exposure limits, respiratory protection with an organic vapour cartridge or supplied air is required.
| OSHA PEL, United States | 500 ppm as an 8-hour time-weighted average, 2000 mg/m3 |
| ACGIH TLV-TWA | 400 ppm as an 8-hour time-weighted average |
| NIOSH IDLH | 750 ppm |
| GHS hazard classes | Flammable liquid category 2, aspiration hazard category 1, specific target organ toxicity single exposure category 3 for narcotic effects |
| Typical alarm setting | 10 percent of the lower explosive limit for flammable gas detection |
Safe Handling, Storage and Spill Response
Store in a cool, dry, well-ventilated area away from heat, sparks, flames, and strong oxidisers, ideally below 30 °C and out of direct sunlight.
Keep containers closed when not in use and keep only the quantity needed for a shift in the working area. Bulk tanks should be earthed and fitted with vapour recovery where required.
Use local exhaust ventilation and work only in areas free of ignition sources. Never use n-heptane in a confined space without gas testing and a permit.
Wear chemical-resistant gloves, splash goggles or a face shield, and antistatic protective clothing. Confirm glove material compatibility with the glove supplier before use.
Contain small spills with inert absorbent, move the material to a labelled hazardous waste container, and ventilate the area. Prevent the liquid from entering drains, basements, or watercourses.
For large releases, evacuate, eliminate ignition sources, and use foam or dry chemical extinguishing media. Water spray may be used to cool containers but can spread a burning pool and is not a suitable extinguishing agent on its own.
Frequently Asked Questions
Q: Is n-heptane toxic to humans?
n-Heptane has low acute toxicity and is not classified for acute oral, dermal, or inhalation toxicity, but high vapour concentrations cause narcotic effects and the liquid is an aspiration hazard if swallowed or inhaled into the lungs.
Q: What is the CAS number and formula of n-heptane?
The CAS number is 142-82-5 and the molecular formula is C7H16, with a molar mass of about 100.2 g/mol.
Q: What are the symptoms of n-heptane exposure?
Inhalation causes cough, sore throat, and shortness of breath, progressing to headache, dizziness, and drowsiness at higher concentrations. Skin contact causes dryness and dermatitis, and ingestion causes nausea and vomiting.
Q: Is n-heptane flammable?
Yes. It is a category 2 flammable liquid with a flash point near -4 °C, and its vapour forms explosive mixtures with air over roughly 1.0 to 6.7 percent by volume.
Q: What is the workplace exposure limit for n-heptane?
OSHA sets a permissible exposure limit of 500 ppm as an 8-hour time-weighted average, and ACGIH recommends a threshold limit value of 400 ppm over the same period.
Q: How should n-heptane be stored and handled?
Keep it below 30 °C in closed, grounded containers in a ventilated area free of ignition sources and separated from strong oxidisers, and use local exhaust ventilation plus chemical-resistant gloves and goggles during handling.
Q: What is n-heptane used for?
It is used as the zero reference for octane number measurement, and as a solvent, laboratory reagent, and raw material for organic synthesis and pharmaceutical intermediates.