What are the boiling point and density of n-Butane? What hazardous characteristics are indicated in its MSDS?
n-Butane (C₄H₁₀, CAS 106-97-8) has a boiling point of -0.5°C, which means it vaporizes very easily at room temperature. Its vapor density is approximately twice that of air (relative density 2.05), so after a leak it tends to accumulate on the ground and in low-lying areas. Its core hazardous characteristics include: extremely flammable (R12), easily forming explosive mixtures with air; having narcotic and asphyxiating effects, with high-concentration inhalation potentially causing unconsciousness; and its vapor is heavier than air, which can lead to flashback upon contact with an ignition source - a primary factor in secondary injuries. When storing, it must be kept away from heat and ignition sources, with the storage temperature controlled below 30°C.
Chapter 1: Quick Reference Table of n-Butane's Physicochemical Properties
n-Butane is a common saturated alkane with the chemical formula C₄H₁₀ and CAS number 106-97-8. The following are its core physical and chemical parameters:
1.1 Basic Physical Constants
| Parameter | Value | Remark |
|---|---|---|
| Molecular Weight | 58.12 | - |
| Melting Point | -138.4°C | Extremely low melting point |
| Boiling Point | -0.5°C | Slightly below the freezing point of water; vaporizes rapidly at room temperature |
| Relative Density (Gas) | 2.05 (air = 1) | Approximately twice as heavy as air |
| Relative Density (Liquid) | 0.58 (water = 1) | Lighter than water; floats on the surface |
| Flash Point | -60°C | Extremely low; highly flammable |
| Autoignition Temperature | 287°C | Can ignite without an open flame at high temperatures |
| Explosion Limits | 1.5%~8.5% (by volume) | Wide range; high risk |
Data shows that the boiling point of n-Butane is -0.5°C, which means even in the harsh cold of northern winters, it can quickly volatilize into a gas. Its vapor density is twice that of air, so after a leak, it will "sink" to the ground like water and flow into low-lying areas and sewers.
1.2 Other Properties
Solubility: Readily soluble in water, alcohol, and chloroform - this property allows it to be mutually soluble with various solvents when used as an aerosol propellant.
Appearance and Odor: Colorless gas; pure product is odorless, while industrial grades typically have a slight unpleasant odor (similar to gasoline).
Critical Parameters: Critical temperature 151.9°C, critical pressure 3.79 MPa - this means that n-Butane cannot be liquefied by pressurization above 151.9°C.
Chapter 2: Core Interpretation of n-Butane MSDS - Why Is It Dangerous?
The MSDS (Material Safety Data Sheet) is the "catalog" for assessing the hazards of chemicals. Based on the MSDS data for n-Butane, we have extracted three core risk points:
2.1 Health Hazards: Narcotic and Asphyxiating Effects
n-Butane is a low-toxicity substance, primarily entering the body through inhalation.
Acute poisoning: In high-concentration environments, n-Butane displaces oxygen in the air, leading to oxygen deficiency. Initial symptoms include dizziness, headache, drowsiness, nausea, and a drunken state. In severe cases, rapid unconsciousness can occur.
Chronic effects: Long-term exposure may cause headaches, poor sleep, fatigue, and other symptoms.
Occupational exposure limit: TLV-TWA is 800 ppm (approximately 1900 mg/m³).
First aid measures: If inhaled, the affected person must be immediately moved to fresh air. If breathing stops, administer artificial respiration immediately and seek medical attention.
2.2 Fire and Explosion Hazard: Extremely Flammable and "Flashback"
This is the most fatal danger of n-Butane.
Extremely flammable (R12): The flash point is as low as -60°C, meaning that under most ambient temperatures, it is "ready to ignite" at any moment.
Strong explosiveness: The wide explosion limit range (1.5%~8.5%) means that even a slight leak can easily reach explosive concentrations.
Flashback: The MSDS particularly emphasizes - gas is heavier than air and can spread a considerable distance to low-lying areas, where it can cause flashback upon contact with an ignition source. This is the most common cause of "secondary accidents" in n-Butane leak incidents: the leaked gas spreads along the ground to a distant ignition source, and the flame instantly travels back along the gas trail to the leak point.
Firefighting methods: Shut off the gas source! If the gas source cannot be shut off, absolutely do not extinguish the flame at the leak point. Instead, spray water to cool the container, and use water spray, foam, carbon dioxide, or dry chemical powder for firefighting.
2.3 Reactivity: Incompatible Materials
n-Butane is relatively chemically stable, but it can react violently, even explosively, upon contact with strong oxidizers (such as chlorine, oxygen, and calcium hypochlorite). During storage, it must be strictly separated from oxidizers and halogens.
Chapter 3: Safe Storage, Transport, and Leak Emergency Response
3.1 Storage Requirements
According to the MSDS and operating specifications, n-Butane storage must meet the following conditions:
| Requirement Category | Specific Content |
|---|---|
| Warehouse | Cool, well-ventilated, dedicated flammable gas warehouse |
| Temperature | Warehouse temperature not exceeding 30°C |
| Humidity | Relative humidity not exceeding 80% |
| Explosion-Proof Facilities | Lighting and ventilation must be explosion-proof; tools that can generate sparks are prohibited |
| Prohibited Mixed Storage | Must not be stored with oxidizers or halogens |
| Static Protection | Cylinders and containers must be grounded and bonded to prevent static accumulation |
3.2 Transport Requirements
Safety caps must be worn during cylinder transport; cylinders should be laid flat with valves facing the same direction.
Must not be loaded or transported with oxidizers.
Transport should be conducted in the morning or evening during summer to prevent sunlight exposure.
3.3 Leak Emergency Response
In the event of a leak, follow these steps:
Quickly evacuate personnel to an upwind location and strictly control access.
Cut off and eliminate all ignition sources.
Emergency responders should wear self-contained positive-pressure breathing apparatus and anti-static work clothing.
Cut off the leak source if possible.
Cover nearby sewers and other low-lying areas with industrial covers or absorbent to prevent gas entry.
Provide adequate ventilation to accelerate dispersion.
Spray water spray to dilute and dissolve (Note: Water cannot stop combustion but can reduce gas concentration).
If possible, use an exhaust fan to vent the leaked gas to an open area or install a flare to burn it off.
Chapter 4: Safety Precautions in Common Applications
4.1 Lighters and Portable Gas Canisters
Ordinary disposable lighters store a small amount of liquid butane. Although they are pressure-resistant by design, they should still not be left on car dashboards or in other high-temperature, sun-exposed areas to prevent pressure build-up and bursting.
4.2 Laboratory and Industrial Standard Gases
High-purity n-Butane (99.99%) is used for standard gases and calibration gases. When using cylinders, operations should be conducted inside a fume hood, kept away from open flames and spark-producing equipment, and the cylinder must be secured to prevent tipping.
4.3 Refrigerant R600
When n-Butane is used as refrigerant R600, the precautions during maintenance include: Never apply flame or welding to a leaking refrigeration system. The system must first be evacuated and purged with nitrogen.
Conclusion: Know n-Butane, Respect n-Butane
The physical properties and hazardous characteristics of n-Butane can be summarized by three key words: boiling point -0.5°C (easy vaporization), vapor density twice that of air (easy accumulation), flash point -60°C (highly flammable). These characteristics determine its widespread industrial applications, but also dictate that we must handle its storage, transport, and use with professionalism and rigor.
Whether purchasing, using, or transporting n-Butane, it is recommended that operators undergo specialized training and strictly follow operating procedures. There are no small matters when it comes to safety, especially when dealing with a gas that is "invisible and intangible" but can ignite instantly - a sense of caution is absolutely necessary.
