The P ratings indicate the protection against particles. P1 is the lower or basic level of protection (with or without valve). There is also a P2 for medium or intermediate protection (with or without valve) and P3 is the highest level of protection (only available with a valve). The valve reduces heat and moisture build-up to increase comfort and safety for the wearer. But there is a lot more to respiratory protection than just opting for a P1, P2 or P3.
I am assuming that because you were given a P1 mask, you are working with solids or liquids and not gases. P1 should not be used as protection against fumes and P2 can only be used against fumes if the manufacturer declares it is safe to do so.
But, before you reach for any type of face mask, remember that all other reasonably practical measures should be used to control exposure. Personal protective equipment (PPE) and respiratory protective equipment (RPE) should be the last, not the only, option. For instance, if you are using a stone or disc cutter to slice through concrete or paving slabs, you need to consider using dust suppression equipment to reduce the level of dust in the first place.
You should also be aware of warning symbols on products - the skull and cross bones indicating toxic substance or symbols classifying the product as an irritant, corrosive, radioactive or biological agent. You should wear RPE if the substance is a dust of any kind with an airborne concentration of more than 4mg/cu m as respirable dust or more than 10mg/cu m for inhalable dust.
What type of RPE you need depends on the type of hazard. The level of protection needed depends on the severity of the hazard presented by the substance, the amount of substance and the ease with which it can be breathed in. The hazard, amount of substance and level of hazard must be assessed and the risk to your respiratory system considered - along with the risk to eyes and skin. The wearer's needs must be taken into account, as must workplace conditions.
Health & Safety Executive (HSE) guide HSG53 Respiratory Protective Equipment at Work: A Practical Guide is useful. It can be downloaded from the HSE website for free and includes a form to help record details of the workplace environment, work factors, the substances involved, task-related factors and details of the wearer. It helps with decisions concerning dustiness and volatility and then with deciding what level of protection is required.
RPE must be adequate and provide the user with effective protection. It must be suitable for the intended use, be CE-marked and be selected, used and maintained by properly trained people. It must also be correctly examined and tested and needs to be stored in the correct way.
Selecting the correct PPE or RPE for any task requires a degree of knowledge, experience and competence. If you are in any doubt about any aspect of product selection, you should seek advice from safety consultants, manufacturers or supplies, or from the relevant trade organisations.
Health & Safety at Work Act, Management of Health & Safety at Work Regulations and Control of Substances Hazardous to Health Regulations.