Which paint cans do not require pressure release before opening?

I. Atmospheric Pressure Open-Top Paint Cans

1. Ordinary Small Capacity Open-Top Plastic Cans: HDPE open-top paint cans of 1L or less for everyday household use. These are not pressure-sealed at the factory, and the internal and external pressures are always balanced. No pressure release is required before opening.

2. Screw-Cap Ordinary Water-Based Paint Cans: These are standard small buckets of water-based latex paint for home use. They use ordinary screw caps for sealing. There is no excess evaporation pressure inside the can; simply screw it open counterclockwise.

3. Temporary Refill Open-Top Containers: Leftover paint transferred from a large container to an unpressurized open-top container does not require pressure release before opening.

II. Special Structure Unpressurized Paint Cans

1. Special Paint Cans with Vent Valves: These cans have a built-in one-way vent valve that automatically balances internal and external pressures, preventing pressure buildup. No pressure release is required before opening.

2. Completely emptied paint cans: No residual paint or volatile gases are present inside; the internal and external pressures are identical. No pressure release is required before opening.

3. Unpressurized manual stirring paint cans: Small paint cans that rely solely on manual stirring and lack a sealed, pressure-bearing design. No pressure buildup occurs during the entire process, and no pressure release is required before opening.

III. Paint cans in specific conditions

1. Cans recently opened and reopened: Cans that have been completely opened previously, have less than 1/3 of the paint remaining, and were stored at a stable temperature. No high pressure will form inside, and no pressure release is required.

2. Full cans of new paint stored at a constant temperature: Brand new, full cans of ordinary paint stored at approximately 20°C in a cool, shaded place without any shaking or temperature fluctuations. They can be used directly before opening.

3. Specialty paint cans without volatile components: Water-based mineral paints and inorganic coatings that do not contain volatile organic solvents produce almost no volatile gases. There is no additional pressure inside the can, and no pressure release is required.