Hazardous Materials Otsu-4 | Applied Physics, Chemistry, and Fire Prevention Cases

Gasoline vapour is heavier than air and can travel along the floor into low spots and depressions. A pit away from the leak may therefore become hazardous. The non-explosion-protected pump must not be energised; ignition sources should be controlled, and ventilation and concentration testing must cover low areas. Ceiling exhaust alone does not demonstrate safety.

Flash point indicates the temperature at which enough vapour can form to burn when an external flame or spark is present. It is different from autoignition temperature. At 20°C, gasoline is far above its flash point, so a static spark can ignite its vapour even though the liquid is neither boiling nor near 300°C.

Although 8.5% is above the representative upper flammable limit, dilution with air takes the concentration through the 7.6% to 1.1% flammable range. Being too rich at the instant of measurement does not make the ventilation period safe. Ignition sources, including sparks from ordinary electrical equipment, must be controlled before ventilation begins.

Flow electrification results from contact and separation between the liquid and pipe wall, and charging depends on velocity, materials, and conductivity. A filter can increase charging by increasing contact area. A combined approach is therefore needed: limit liquid-side charging through flow control and reduce potential differences between conductive items through grounding and bonding.

A temperature of 20°C is above the flash points of gasoline and methanol, but below those of xylene and kerosene. Under the stated conditions, gasoline and methanol are therefore the priority pair when judging from flash point alone. This does not make a liquid below its flash point harmless when misting, heating, or other hazards are present.

Higher temperature increases gasoline vapour generation and can raise pressure inside a sealed container. Opening a hot can abruptly may eject vapour or liquid. Ignition sources should be eliminated, the can should be cooled in a safe shaded location, and the container-specific instructions for relieving pressure before opening should be followed.

Below its flash point, an ordinary kerosene surface may not produce enough vapour, but fine droplets dispersed in air can create a combustible mist. Experiments have ignited kerosene mist near 15°C with small spark discharges. A pressurised mist leak cannot be declared safe solely because the ambient temperature is below the flash point.

Gasoline is poorly miscible with water and floats on it. A solid stream directed at the burning surface may spread the burning fuel and enlarge the fire. With an escape route secured and only when incipient firefighting is safe, an extinguisher rated for oil fires should be used. This does not rule out every use of water, such as cooling exposures without striking the fuel surface.

Ethanol is water-soluble, and its effect on foam differs from that of water-immiscible petroleum products, so not every foam has equivalent performance. A concentrate demonstrated for water-soluble liquids and alcohols should be matched against the specific material, installation requirements, approval scope, and manufacturer specifications.

Liquids are difficult to compress but still expand when heated. In blocked-in piping, even a small volume increase can cause a large pressure rise and damage piping, pumps, or fittings. An official accident investigation found that removing a relief valve allowed temperature-driven overpressure to rupture a pump. Protection is required before boiling occurs.