The ability of GCs to evaluate potentially unsafe conditions is similarly mixed. GCs have a high ability to evaluate visible unsafe conditions because it is custom and practice that a GC representative be responsible for the overall jobsite when several subcontractors are working on-site (furthermore, many construction contracts explicitly require that the GC be present when any work is being accomplished, even if only one subcontractor is working). GCs are also expected to observe the jobsite on a frequent basis to ensure that progress and conformance with specifications are satisfactory. On the other hand, GCs also typically have a low ability to evaluate hidden unsafe conditions such as structurally deficient work platforms or hazardous electrical or atmospheric conditions.