Minwax polyurethane is a popular protective clear-coat finish for any type of interior wood. Polyurethane clear-coat is essentially a plastic that is applied as a liquid and dries as a solid plastic sheet. Instead of sinking into the wood grain, polyurethane sits on the surface, forming a protective barrier against moisture. Although safer than many wood-finishing options, a few safety issues still need to be taken into account when using polyurethane.
Like any polyurethane product, Minwax polyurethane clear-coat is highly flammable. It has a flash point of 40.6 degrees Celsius, which means that the liquid can vaporise at that temperature to become an ignited substance. For instance, if the product is used in a closed, hot room and somebody lights a cigarette, the flame from the lighter can cause the polyurethane fumes in the air to ignite at the source of the flame.
The autoignition temperature of Minwax polyurethane is 232 degrees Celsius. This means that if the liquid is exposed to temperatures at least this hot it can catch fire, even without an open flame. This generally happens when the container is stored around hazardous equipment such as kilns and furnaces, but if a fire is already burning in a building where polyurethane is stored, the high ambient temperature will cause the substance to ignite, creating a secondary fire. In case of a polyurethane fire, a dry chemical extinguisher should be used to put it out, and anyone fighting the fire should use a full face shield and respirator.
Minwax polyurethane is non-carcinogenic and cannot enter the bloodstream through the skin, but it does pose some risks to users. The two routes of entry into the body are by ingestion and inhalation. Ingestion can cause severe irritation to the mouth, throat, stomach and intestinal tract, and inhalation can cause irritation to the nose, sinuses, throat and lungs. In cases of ingestion, overexposure can cause nausea and vomiting, and the Poison Control Center should be contacted immediately. Overexposure via inhalation causes dizziness, fatigue and headache, and the victim should be moved to fresh air and brought to the attention of a medical professional.
Although polyurethane will not absorb into the skin, it will dry on the skin's surface and cause dryness and irritation, so any exposed skin should be washed thoroughly after use. Contact with the eyes can cause irritation and blurred vision. Eyes should be flushed with water for 15 minutes, and the injury should be evaluated by a doctor.
The flammability of Minwax polyurethane indicates that it should not be stored near heat or flame. To prevent cases of mistaken identity, the product should always be kept in its original container, which is clearly labelled with the ingredients and hazards. Even empty containers are prone to ignite because of residue and vapours, so they should be disposed of promptly. Chemical disposal methods vary according to local laws, but polyurethane should never be poured down the drain or dumped into sewers.
When using polyurethane, rubber or neoprene gloves should be worn, and hands and arms should be washed with soap and water afterward. Face shields or safety glasses are recommended to prevent splashing into the eyes.