Which type of material is considered an ordinary combustible, with the exception of cellulose nitrates?

The classification of ordinary combustibles includes materials that are typically composed of organic substances and can ignite and sustain combustion. Among the choices, plastics are noted for being ordinary combustibles despite being derived from petroleum products, which can also contain additives that influence their combustibility.

Ordinary combustibles typically encompass materials like wood and other organic matter, which easily ignite and burn when exposed to heat or flames. While some plastics may have high melting points or flame-retardant properties, the common understanding aligns with the broader category of combustibles, which includes them, setting them apart from metals and glass, which are not combustibles at all.

Therefore, identifying plastics as ordinary combustibles—except for cellulose nitrates—demonstrates an understanding of materials that can contribute to fire growth and spread, as they can catch fire under the right conditions and release energy when they combust. This classification is essential for fire safety professionals in assessing risks and implementing appropriate fire prevention measures.