Types of Plastics
The two main forms of plastics likely to be used in schools are thermo-plastics and thermo-setting plastics. Thermo-plastics are formed in a reversible process and can therefore be restored to their original form by the application of heat. They have the flammable hazardous properties of liquids rather than solids, and can also give off toxic fumes at elevated temperatures. Thermo-setting plastics do not have reversible properties and are made by mixing polyester and other polymer resins with appropriate catalysts.
Most resins, accelerators and solvents come within the scope of the Highly Flammable Liquids and Liquefied Petroleum Gases Regulations (1972), which must be strictly observed. The preparation of polyurethane foam and other plastics should only be undertaken in a fume cupboard.
When shaping or cutting plastic materials either by hand or by machine, pupils should wear eye protection, but may also have to wear a suitable dust mask, depending on the nature and scale of the activity and the property of the plastic material. Work should always be carried out in a well ventilated area. Risk assessments should take account of the characteristic of the plastics being worked and where machines are used, for example, the cutting or machining of plastics can cause cutting blades to heat up and melt the plastics, leading to re-warding of the cut and the blade jamming. The use of masking tape along the line of a cut can help prevent this and the effects of acrylic shattering if cut too fast. Hence, slower cutting and feed-in speeds should always be used when possible.
CLEAPSS guidance - MRAT - 053 - Dust and fumes from abrading plastics
CLEAPSS guidance - MRAT - 052 - Abrading and trimming plastics
Uncured Polyester Resin
Uncured polyester resin releases phenylethene fumes. Provided that only small quantities are being used and the area is well ventilated the fumes may not be harmful, but the risk involved depends upon an individual's sensitivity and therefore the context needs to be individually assessed.
Some airborne fibre glass dust particles can cause lung damage and synthetic resins can be harmful to the skin. Suitable PPE should be worn, including disposable gloves, a suitable dust mask, eye protection and apron. Trimming of glass fibre matting (GRP) can be carried out in the open, but not in pupil circulation or play areas. During the hardening/curing process, fumes may be given off, which should not be released into a classroom with pupils present, but instead should be a restricted space during this process. Similarly, there should be no source of combustion present during the construction process and especially when cleaning up.
CLEAPSS guidance - MRAT - 054 - GRP, Resin Casting, chemical and fumes
Polystyrene should never be cut with ordinary knives heated by application to a direct heat source. Cutting polystyrene with a hot wire generates phenylethene fumes. The cutter should be constructed to operate at an even heat, which is just sufficient to cut the material. It is safer to use a battery-operated cutter than one powered by a low-tension supply. Cutting should be carried out only in well-ventilated conditions, for example, near an open window. In casting with other materials, which may have residual water content, it is essential that the material is completely dry before molten metal is introduced. If not the risk of serious explosion is high - see the section on metal casting.
CLEAPSS guidance - MRAT - 057 - Fumes from hot wire cutting of plastics