Celluloid is dangerous for two separate reasons: it burns fast and fiercely because it carries its own oxygen in its nitrate groups, so smothering does not reliably put it out, and it decomposes slowly by itself, releasing acidic gases that speed up the decay and generate heat. Keep any salvaged celluloid in small amounts, cool, ventilated and away from heat, sparks and electrical arcing, and never use it for insulation.
Part of Plastics and Polymers
Celluloid safety covers the fire, fume and self-decomposition hazards of cellulose nitrate plastics and how to store and handle salvaged pieces.
It Burns Because It Carries Its Own Oxygen
Ordinary fuel needs air to burn, and covering it can stop the fire. Cellulose nitrate has oxygen built into its nitrate groups, so once alight it keeps burning with little help from the air. The scratch carrier puts it plainly: it is essentially smokeless powder with a plasticiser, it ignites easily, burns fiercely and cannot be extinguished with water. Treat that as the working rule: do not try to fight a celluloid fire; get away from it. Fire Safety and Suppression states the general rule: fight only a small fire with your exit behind you, otherwise get out.
The softening range of celluloid in the plastics articles is 80-100 °C, and the manufacturing carrier says never to heat it above 150 °C. That leaves 150 - 100 = 50 °C up to 150 - 80 = 70 °C between working temperature and the stated ceiling, a thin margin once hot spots are considered. Treat 150 °C as the outer limit and work at the bottom of the softening range, with hot water or steam, never a flame or a hot plate.
Fire Results In Toxic Fume As Well
Burning or decomposing cellulose nitrate gives off nitrogen oxides and carbon monoxide (general knowledge). Nitrogen dioxide can injure the lungs after a delay of hours, as the corpus notes for the acid fumes in Nitric Acid. Smoke from a celluloid fire is therefore a danger even to people who feel well at first.
It Also Decomposes By Itself
Over years, cellulose nitrate slowly breaks down. The breakdown releases acidic nitrogen oxide gases, and those catalyse further decomposition, so the process accelerates. It also gives off heat. In a small, open, cool piece the heat leaves harmlessly. In a large, packed, warm, closed store it accumulates, and the material can heat itself to ignition with no outside spark. Film stores and archives have been destroyed this way (general knowledge). Residual acid from a poorly washed batch is the commonest starting point: see Nitration Process.
Signs of advancing decay, from general knowledge: yellowing or browning, a sticky or tacky surface, brittleness or crumbling, a sharp acid smell replacing the faint camphor smell, and powder or bubbling on the surface. Camphor loss makes things shrink and warp on its own: see Camphor as Plasticizer.
Rules For Salvaged Celluloid
- Keep small amounts. Heat from decay and the fuel for a fire both scale with the quantity held together.
- Keep it cool and ventilated. Not in an attic, a vehicle, a sealed box or beside a stove. Do not store it airtight.
- Separate it. Keep it away from other combustibles and from solvents, and out of workshops with sparks, furnaces and flames.
- Inspect it. Check periodically for the signs above. A piece that shows them goes outdoors, apart from buildings.
- Never heat, burn, grind or machine it near any ignition source. See Machining Plastics.
- Never use it electrically. It is a thermoplastic that burns where arcing or heat occurs, a bad combination. See Electrical Insulation.
- Never burn it in a stove. It flares.
- If a store fumes, smells sharply of acid or feels warm, leave and keep people clear. Do not enter to fight it.
This article does not give a disposal method, because none is established in the corpus and a wrong one is dangerous. Keep unwanted celluloid out of buildings, and away from heat.
This Is Why The Making Of It Is Left Out
The same compound, made more strongly nitrated, is an explosive, and made badly it is a fire waiting to start. That is the reason Cellulose Nitration, Nitrating Mixture and Nitration Process explain the chemistry and the hazard and stop short of a recipe. The restraint there follows from what is on this page.
Common Mistakes
- Keeping a drawer of old film “for later” — a decaying lot is a fire load.
- Treating a water hose as a solution — the carrier says it cannot be extinguished with water.
- Cutting celluloid on a power tool or a grinder — sparks and friction heat.
- Testing by burning a scrap — that is how fires start.
Fire, fume and self-ignition
Celluloid ignites easily, burns fiercely without outside air, and gives toxic fume. Decomposing celluloid can heat itself to ignition. Keep it in small amounts, cool, open and apart from flame, sparks, heat and electrical arcing. If it catches, do not fight it: clear the area, upwind, and keep everyone back from the smoke.
What’s Next
- Learn next: Lacquers and Coatings — celluloid as a dissolved coating, and the safer alternatives
- Combine with: Celluloid — the material and its history