A cap assembly for enclosing a metallic fastener which extends through a structure, comprising: a housing comprising: an inner wall to position about the metallic fastener and having a first end for abutting the structure and an opposing second end positioned spaced apart from the first end; and an outer wall which extends about and is spaced apart from the inner wall defining a space positioned between the inner wall and the outer wall, wherein at least a portion of a first end of the outer wall is spaced apart from a first plane defined by the first end of the inner wall of the housing and with the first end of the inner wall abutting the structure a flow path is defined from the space through the at least a portion of the first end of the outer wall spaced apart from the first plane; and a plunger member comprising a side wall portion secured to an end wall portion, wherein: the side wall portion of the plunger member has a thickness dimension smaller than a distance between the inner wall and the outer wall to position the side wall portion of the plunger member within the space; and with the side wall portion positioned within the space, the end wall portion is positioned in alignment with the opposing second end of the inner wall and with an opening defined by and through the inner wall, wherein the alignment provides an enclosure provided by the housing and the plunger member in which to contain the metallic fastener. a housing comprising: an inner wall to position about the metallic fastener and having a first end for abutting the structure and an opposing second end positioned spaced apart from the first end; and an outer wall which extends about and is spaced apart from the inner wall defining a space positioned between the inner wall and the outer wall, wherein at least a portion of a first end of the outer wall is spaced apart from a first plane defined by the first end of the inner wall of the housing and with the first end of the inner wall abutting the structure a flow path is defined from the space through the at least a portion of the first end of the outer wall spaced apart from the first plane; and an inner wall to position about the metallic fastener and having a first end for abutting the structure and an opposing second end positioned spaced apart from the first end; and an outer wall which extends about and is spaced apart from the inner wall defining a space positioned between the inner wall and the outer wall, wherein at least a portion of a first end of the outer wall is spaced apart from a first plane defined by the first end of the inner wall of the housing and with the first end of the inner wall abutting the structure a flow path is defined from the space through the at least a portion of the first end of the outer wall spaced apart from the first plane; and a plunger member comprising a side wall portion secured to an end wall portion, wherein: the side wall portion of the plunger member has a thickness dimension smaller than a distance between the inner wall and the outer wall to position the side wall portion of the plunger member within the space; and with the side wall portion positioned within the space, the end wall portion is positioned in alignment with the opposing second end of the inner wall and with an opening defined by and through the inner wall, wherein the alignment provides an enclosure provided by the housing and the plunger member in which to contain the metallic fastener. the side wall portion of the plunger member has a thickness dimension smaller than a distance between the inner wall and the outer wall to position the side wall portion of the plunger member within the space; and with the side wall portion positioned within the space, the end wall portion is positioned in alignment with the opposing second end of the inner wall and with an opening defined by and through the inner wall, wherein the alignment provides an enclosure provided by the housing and the plunger member in which to contain the metallic fastener.