Many types of flame-resistant cable exhibit "cold flow" of the inner sheath bedding, which could have adverse effects on the protection of the apparatus.
Where such cable is used, it is a requirement of EN 60079-14 and IEC 60079-14, clause 9-1-3 to employ a suitable cable entry device. The code of practice clearly states that "a cable gland employing a compression (displacement) seal should not be used on cable exhibiting cold flow characteristics".
"Cold flow" can be more fully described as thermoplastic materials which flow when subjected to pressure at ambient temperature, i.e. the inner sheath bedding material will flow away from any pressure applied to it, including that of a cable gland inner seal of the compression or displacement type, the effect being that there may no longer be an effective seal on the inner sheath of the cable.