ISSA is the marine stores coding system built by ship suppliers themselves, running in parallel to IMPA. Knowing both means an order never stalls because one supplier only recognises one system.
What ISSA actually is
ISSA, the International Ship Suppliers and Services Association, maintains its own marine stores catalogue and coding system, built and updated by the supplier side of the industry rather than the purchasing side that created IMPA. The two systems overlap heavily in what they cover but use different numbering, so a part identified under one code needs translating before a supplier working the other system can quote it.
In practice, most ship chandlers and purchasing platforms support both codes side by side, and a competent supplier keeps a cross-reference so a request in either format resolves to the same physical item.
When ISSA matters more than IMPA
Some European and Mediterranean suppliers historically built their catalogues around ISSA first, so a purchasing order that only carries an IMPA number can slow down at that specific supplier while their staff look up the equivalent. Carrying both codes on a purchase order removes that lookup step entirely.
For provisions and consumables in particular, where regional suppliers dominate the market, quoting the ISSA code alongside the IMPA code is the more reliable habit, not the exception.
Finding the right ISSA number
The ISSA marine stores guide is organised by product category in the same broad structure as IMPA, covering deck stores, engine stores, provisions, cabin and galley equipment, and safety items, so a search by category narrows the list quickly even without knowing the exact number in advance.
Where a part has both codes published, quoting them together in a purchase order is the single habit that prevents the most common cause of a delayed quote: a supplier system that only recognises one numbering convention.
The short answer
ISSA and IMPA are parallel, not competing, systems. Quoting both codes on a purchase order, when both are available, is what keeps an order moving regardless of which numbering convention a given supplier's system was built around.