Hazchem codes

Anyone who has been on a road in the UK has probably seen the strange, cryptic, orange signs affixed to the back of many lorries and trucks. They seem to warning us about what the vehicle is carrying, but what do all those apparently random letters and numbers actually mean? More importantly, when should you rush to help the victims of a tanker accident, and when should you leave them to die a horrible death in a bath of acid?

The sign itself looks (very approximately) like this:

        
+-----------------------+--------------+
|     .              (1)|           (2)|
|    /|  \        /     |   _      _   |
|     |   \  /\  /      |  \#\    /#/  |
|    ---   \/  \/       |   \#\  /#/   |
+-----------------------+    \#\/#/    |
|   ___   ____   ___ (3)|     >##<     |
|      \     /  /___    |    /#/\#\    |
|   ---<    /       \   |   /#/  \#\   |
|   ___/   /    ____/   |  /#/    \#\  |
+-----------------------+-------+------+
|SPECIALIST ADVICE:          (4)|   (5)|
|                 01226 457 111 |  E2  |
+-------------------------------+------+

Each of the five sections has its own purpose.

(1) The emergency action code

This consists of one digit and up to four letters. The meanings of the numbers are as follows:

• 1 - coarse spray
• 2 - fine spray
• 3 - foam
• 4 - dry agent

This describes the form the contents takes. "Dry agent" means that water must not come into contact with the substance.

The letters specify what precautions should be taken, and how spillage should be dealt with:

Letter   Explosive | Protection  | Disposal
===================+=============+==========
| P       yes      | splash suit | dilute  |
+------------------+             |         |
| R       no       | splash suit | dilute  |
+------------------+-------------+         |
| S       yes      | fire suit   | dilute  |
+------------------+             |         |
| T       no       | fire suit   | dilute  |
+------------------+-------------+---------+
| W       yes      | splash suit | contain |
+------------------+             |         |
| X       no       | splash suit | contain |
+------------------+-------------+         |
| Y       yes      | fire suit   | contain |
+------------------+             |         |
| Z       no       | fire suit   | contain |
+------------------+-------------+---------+

Here, splash suit refers to "liquid tight chemical protective clothing", while fire suit refers to "positive pressure compressed air breathing apparatus in conjunction with tunic, overtrousers and gloves."

Dilute means that the spillage can be washed into drains, although excessive contamination should be avoided, whereas contain means that the substance cannot be allowed to enter any drains ot watercourses.

(2) The hazard warning sign

This is the really interesting one. The actual sign takes the form of a diamond box with a gory picture showing what will happen if the truck crashes.

There are 13 different classes, ranging from the innocuous "elevated temperature substances" through to "fissile radioactive material". The substance is not only rated on general characteristics: flammability is subclassed into flammable gases, flammable liquids, flammable solids and spontaneously combustable to name a few.

It is in this section that specific dangers such as corrosion or toxicity are listed. A complete list:

• Class 1: Explosive substance or articles
• Class 2: Gases
• Class 3: Flammable liquids
• Class 4.1: Flammable solids, self-reactive and desensitised explosive
• Class 4.2: Substances liable to spontaneously combust
• Class 4.3: Substances which, in contact with water emit flammable gases
• Class 5.1: Oxidizing substances
• Class 5.2: Oxidizing peroxides
• Class 6.1: Toxic substances
• Class 6.2: Infectious substances
• Class 7: Radioactive material
• Class 8: Corrosive substances
• Class 9: Miscellaneous dangerous substances and articles
• Other: Elevated Temperature Substances, Marine Pollutant

(3) The UN number

This is a numeric code which is supposed to identify this substance uniquely. The purpose of it is so that emergency services can offer some exact information about the spillage, rather than vague descriptions like "it smells funny".

(4) The Specialist Advice phone number

This is the number emergency services should call if an accident occurs. Information from the previous three sections can then be relayed and a course of action recommended.

(5) The company logo

They say that any advertising is good advertising, and this section keeps the PR people happy by associating a company with the gallons of lethal, fluorescing green nuclear waste seeping into the water table. Also, identifying from where this truck originated could help verify the dangers.

Conclusion

There are a number of urban myths about a charitable bystander running to rescue drivers from crashed tankers, only for the vehicle's contents to dissolve the good Samaritan before they reach the cab, leaving only a gold wedding ring. Well now there really is no excuse - either memorise this writeup or get a Hazchem scale card from the National Chemical Emergency Centre!

See also: poison