A powered air purifying respirator (PAPR) module comprising: a housing having a central axis and formed by an upper cylindrical portion and a lower cylindrical portion; a fan mounted in the lower cylindrical portion, a motor mounted in the housing and operably connected to the fan for driving the fan, and at least one battery mounted within the housing and operably connected to the motor for powering the motor; an inlet defined by an internal sleeve in the upper cylindrical portion in fluid communication with the fan and configured to selectively receive a filter canister for filtering air that is drawn into the inlet; and an outlet defined by an external sleeve in the lower cylindrical portion and in fluid communication with the fan; characterized in that: a lower body cover in the lower cylindrical portion seals a breathing zone in the lower cylindrical portion from an enclosed space in the upper cylindrical portion; the at least one battery is mounted in the enclosed space in the upper cylindrical portion; the fan and motor are in the sealed breathing zone, which is in fluid communication with the inlet and the outlet, wherein the inlet and the outlet are coaxially aligned, and wherein the outlet is adapted to mount the housing to a facepiece of a respirator mask or to a conduit that is fluidly connected to a facepiece inlet opening in a respirator mask; whereby the modular PAPR can be positioned between a filter canister and a respirator mask or between a filter canister and a conduit that is connected to a respirator mask. a housing having a central axis and formed by an upper cylindrical portion and a lower cylindrical portion; a fan mounted in the lower cylindrical portion, a motor mounted in the housing and operably connected to the fan for driving the fan, and at least one battery mounted within the housing and operably connected to the motor for powering the motor; an inlet defined by an internal sleeve in the upper cylindrical portion in fluid communication with the fan and configured to selectively receive a filter canister for filtering air that is drawn into the inlet; and an outlet defined by an external sleeve in the lower cylindrical portion and in fluid communication with the fan; characterized in that: a lower body cover in the lower cylindrical portion seals a breathing zone in the lower cylindrical portion from an enclosed space in the upper cylindrical portion; the at least one battery is mounted in the enclosed space in the upper cylindrical portion; the fan and motor are in the sealed breathing zone, which is in fluid communication with the inlet and the outlet, wherein the inlet and the outlet are coaxially aligned, and wherein the outlet is adapted to mount the housing to a facepiece of a respirator mask or to a conduit that is fluidly connected to a facepiece inlet opening in a respirator mask; whereby the modular PAPR can be positioned between a filter canister and a respirator mask or between a filter canister and a conduit that is connected to a respirator mask. a lower body cover in the lower cylindrical portion seals a breathing zone in the lower cylindrical portion from an enclosed space in the upper cylindrical portion; the at least one battery is mounted in the enclosed space in the upper cylindrical portion; the fan and motor are in the sealed breathing zone, which is in fluid communication with the inlet and the outlet, wherein the inlet and the outlet are coaxially aligned, and wherein the outlet is adapted to mount the housing to a facepiece of a respirator mask or to a conduit that is fluidly connected to a facepiece inlet opening in a respirator mask; whereby the modular PAPR can be positioned between a filter canister and a respirator mask or between a filter canister and a conduit that is connected to a respirator mask.