The recent events in China highlight the challenges that on & offsite emergency response teams face when tackling an incident at a high hazard facility.
We already have the GHS symbols which provide 'universal' information about hazards to workers using chemicals under normal conditions of use, but do we need a more international representation of the hazards that may occur during emergency response i.e. abnormal conditions?
The NFPA 704 'Fire Diamond' provides a standard system for identifying the hazards of materials during emergency response, however this is only applicable in North America and a few other jurisdictions (e.g. The Netherlands - I'd welcome some feedback on where else it is used) and only considers the effects at normal temperature and pressure.
These are classified as follows using a scale of 0 (non-hazardous) to 4 (extremely hazardous):
At the very least, it makes sense for NFPA 704 to be adopted more widely and perhaps consider expanding it not just to indicate the nature but also the scale of the hazard which will be affected by the storage/operating conditions - particularly pressure & temperature.
May I suggest adding these parameters to the diagram, which then becomes a 'Hazard Hexagon' rather than a Danger (or simply Fire) Diamond.
 > 100 barG (1500 psi)
 10 - 100 barG (1500 psi)
 1 - 10 barG (150 psi)
 0 - 1 barG (15 psi)
[-1] -1 (FV) to 0 barG
These are somewhat subjective values based on standard pipe ratings (ANSI) and temperature classification (IEC). I've tried to capture negative conditions such as vacuum and cryogenic as well. The 60 oC figure is a typical PP insulation value, in case you were wondering.
It may also be appropriate to include the potential inventory that may be released e.g. within a storage tank or between isolation valves but not only does this make a more cluttered heptagon but this information is typically already shown on the outside of tanks anyway.
These hexagons could also be added to PFD (P&ID's may become too messy), Heat & Mass Balances, Operating Instructions, Permit-to-Work and even the Top Event of BowTies to act as simple, visual reminders to plant personnel not to become complacent about the dangers they interact with daily.
Finally, it is good practice (and in many jurisdictions a regulatory requirement) to have in place (and rehearse) an emergency response plan which gives the emergency services and the site the opportunity to practice their response...but does this cover every shift of the site and response team?, so it is likely that on any single 'shout' that members of one or both teams has not actually rehearsed their activities. Perhaps by prominently displaying these on the plant it may be clearer to even an 'unrehearsed' team what they are facing.
I look forward to all comments (particularly where such as system or similar has already been adopted).