IMDG Code defines polymerizing substances as “substances which, without stabilization, are liable to undergo a strongly exothermic reaction resulting in the formation of larger molecules or resulting in the formation of polymers under conditions normally encountered in transport.”

Such substances are considered to be polymerizing substances of class 4.1 when their self-accelerating polymerization temperature (SAPT) is 75°C or less under the conditions (with or without chemical stabilization as offered for transport) and in the packaging, IBC or portable tank in which the substance or mixture is to be transported; Substances meeting the criteria of a polymerizing substance and also for inclusion in classes 1 to 8 are subject to the requirements of special provision 386 [IMDG Code 2.4.2.5.1]

Polymerizing substances will require temperature control in transport if their self-accelerating polymerization temperature (SAPT) is:

• packaging or IBC, 50°C or less
• portable tank, 45°C or less

Definition in chapter 1.2.1 of the Code defines Self-accelerating polymerization temperature (SAPT) means the lowest temperature at which polymerization may occur with a substance in the packaging, IBC or portable tank as offered for transport. The SAPT shall be determined in accordance with the test procedures established for the self-accelerating decomposition temperature for self-reactive substances in accordance with part II, Section 28 of the Manual of Tests and Criteria.

Special Provision 386

When substances are stabilized by temperature control, the provisions of 7.3.7 apply. When chemical stabilization is employed, the person offering the packaging, IBC or tank for transport shall ensure that the level of stabilization is sufficient to prevent the substance in the packaging, IBC or tank from dangerous polymerization at a bulk mean temperature of 50°C, or, in the case of a portable tank, 45°C.  

Where chemical stabilization becomes ineffective at lower temperatures within the anticipated duration of transport, temperature control is required. In making this determination factors to be taken into consideration include, but are not limited to, the capacity and geometry of the packaging, IBC or tank and the effect of any insulation present, the temperature of the substance when offered for transport, the duration of the journey and the ambient temperature conditions typically encountered in the journey (considering also the season of year), the effectiveness and other properties of the stabilizer employed, applicable operational controls imposed by regulation (e.g. requirements to protect from sources of heat, including other cargo transported at a temperature above ambient) and any other relevant factors. (IMDG Code 38-16 – Update 2 – Polymerizing Substances)

SP 386 puts the onus on “the person offering the packaging, IBC or tank” and also refers to chapter 7.3 section 7.3.7 for temperature control. Chapter 7.3 section 7.3.1 states “This chapter contains the provisions appropriate to those responsible for the consignment operations in the dangerous goods transport supply chain, including provisions relating to packing of dangerous goods into cargo transport units.”

International Chamber of Shipping (ICS) had pointed out to IMO that these two different wordings (the person offering and those responsible for the consignment operations) can result in confusion as to who is finally responsible for the compliance to SP 386 as shipper/consignor named in the dangerous goods declaration may not be the manufacturer or the supplier offering the packaging.

Some of the instances noticed about confusion and or lack of sufficient information required for safe carriage:

• Carrier ask the SP 386 confirmation to tank operator
• Tank operator ask the shipper -shipper inform it is your tank (package) so you need to confirm
• Shipper ask manufacturer/supplier – they reply we are not transporting
• Shipper ask what to confirm – carrier/tank operator copy paste SP 386 to shipper
• Shipper write a mail “Yes we confirm our shipment meets the provisions of SP 386….”
• Carrier ask by email “Please conform booking confirms to SP 386” – Shipper replies “YES”
• Some shippers give a confirmation SAPT is > 51 Deg C
• Some confirm SAPT is 51 Deg C for 80-90 days transit
• Some carrier ask only when transported in tanks, not for packagings and IBCs
• Some shipper confirms xyz inhibitor content xx grams/kg

A mere confirmation by email or in letter head “yes we confirm to SP 386” may not be sufficient for safe transport of these substances.

Nothing in the IMDG Code states that a shipper and NVOCC may not provide additional information

United States District Court: Re M/V MSC Flaminia

Shipper should provide full and adequate information to carrier; carrier should monitor the transit and ensure it is safe especially when encountering unexpected delays and take necessary actions when needed. Read TT Club’s TT Talk – Safety in abnormal conditions.

What shipper should inform?

ICS had proposed to IMO that “a simple confirmation from the shipper/consignor that the polymerizing substance is stabilized in accordance with SP 386 may not always be sufficient to help secure the safety of the crew and the vessel at sea, due to the discrepancies identified...” and further suggested “shipper/consignor to specify and confirm the following in dangerous goods declaration

1. indication of the SAPT
2. that the chemical inhibitors employed are sufficient for the anticipated duration of transport and expected ambient temperatures during sea transport, as well as transhipment; and

•  that no temperature control is necessary; or
•  if a temperature control is required, the kind of cooling requirements/container type used, as applicable, in accordance with section 7.3.7.3.2 of the IMDG Code [ICS submission to IMO]