Page 242 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

Once inerted, the tank should be kept topped-up as necessary to ensure
that a positive pressure is maintained and the oxygen content does not
---ใช้เพื่อการศึกษาเท่านั้น---
exceed 8% by volume.

The exhaust vapour from the tank during inerting should be ventilated
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
through an opening at least 2 metres above the deck. Portable
standpipes should be used where necessary.

Double hull tanks are not usually fitted with devices such as P/V valves
which allow a positive pressure to be maintained in the tank. The
guidelines and procedures referred to above and in Section 11.4.7 should
address the sealing of openings that might let air into the tank and the
method for ensuring that the tank cannot be over-pressurised.

The progress of inerting can be monitored by measuring the oxygen
content of the exhaust vapour. However, atmosphere measurements to
determine when the tank is fully inert, and subsequent monitoring
measurements, must be taken at all designated sampling points and with
the inert gas supply stopped.

11.8 Cargo Measurement, Ullaging, Dipping and

Sampling
ึ
11.8.1 General

Depending on the toxicity and/or volatility of the cargo, it may be
necessary to prevent or minimise the release of vapour from the cargo
tank ullage space during measurement and sampling operations.

Wherever possible, this should be achieved by the use of closed gauging
and sampling equipment.

There are circumstances where it is considered essential to obtain clean
samples for quality purposes, such as for high specification aviation fuels.
The use of closed sampling equipment may cause cross-contamination of
product samples and, where this is the case, the terminal operator may
wish to undertake open sampling. A risk assessment should be carried
out to ascertain whether open sampling can be achieved safely, taking
into account the product volatility and toxicity. Risk mitigation measures,
including the use of appropriate personal protective equipment if
necessary, should be put in place before starting the operation.

Closed gauging or sampling should be undertaken using the fixed
gauging system or by using portable equipment passed through a vapour
lock. Such equipment will enable ullages, temperatures, water cuts and
interface measurements to be obtained with a minimum of cargo vapours
being released. This portable equipment, passed through vapour locks, is
sometimes referred to as ‘restricted gauging equipment’.

When it is not possible to undertake closed gauging and/or sampling
operations, open gauging will need to be employed. This will involve the
use of equipment passed into the tank via an ullage or sampling port or a
sounding pipe, and personnel may therefore be exposed to
concentrations of cargo vapour.

208 © ICS/OCIMF/IAPH 2006