(5)Sub-rule (2) shall not apply to specially constructed steel tank motor vessel approved by the Chief Controller which are engaged in the transport of petroleum in bulk on such rivers and on such ports thereof as may be approved by him in areas outside port limits, or by the Conservator within port limits, if the tanks of such vessels are securely fastened down immediately after unloading and the vessels depart not later than 12 hours after completion of unloading for their next place of loading.
