Segregation of hazardous materials

This Technical Measures Document refers to issues surrounding the storing and segregation of hazardous materials and how it can be used to minimise the foreseeable risks of a major accident or hazard.

The relevant Level 2 Criterion is 5.2.1.3(29)c, g.

General principles

The following aspects should be considered with respect to the Segregation of Hazardous Materials:

• Human factors;
• Poorly skilled work force;
• Ignorance towards physical and chemical properties of stored substances;
• Unconscious and conscious incompetence;
• Plant lay-out; and
• Plant siting.

The following issues may contribute towards a major accident or hazard:

• Failure to understand the properties of substances handled;
• Failure to identify hazards associated with mixing substances and domino events;
• Failure of quality assurance procedures;
• Insufficient recording of chemical inventories at each location on site;
• Insufficient labelling of chemical storage containers (raw materials, reactants, intermediates, products, by-products and waste);
• Poor warehousing management systems;
• Poor house keeping.

Contributory factors for an assessor to consider concerning all aspects of Segregation of hazardous materials

The Safety Report should address the following points:

• Whether formal hazard identification and risk assessment has been used to determine the need for segregation (e.g. HAZOP, HAZAN, QRA);
• Whether there is a chemical inventory system sufficient to address and categorise hazardous materials into compatible groups;
• Whether there is a sufficient site plan illustrating a compact block layout system with designated zones/plots for compatible hazardous materials (zones 0, 1 & 2, oxidising agents, flammable substances, explosive substances, strong acids, cyanide compounds, LPG);
• Whether hazardous areas are classified and sufficient to segregate compatible, hazardous materials to avoid overlap of these areas. (oxidising agents and flammable substances areas should not overlap, strong acids and cyanide compound areas should not overlap, peroxides should not be stored near any metallic compounds that could cause decomposition and the liberation of oxygen);
• Whether sufficient areas have been designated for hazardous substances with low flash points (Class I, II(1), II(2), III(1) & III(2) see the Further Reading section at the end of this page relating to the Refining Safety Code and Basic Classification of Flammable and Combustible Liquids);
• Whether there are sufficient warning signs in place to inform employees and visitors of the potentially, hazardous environments they are approaching (no smoking signs, flammable area, intrinsically safe zone);
• Whether there are sufficient traffic routes for the emergency services to safely access and egress a hazardous area in the event of an emergency;
• Whether the emergency services are aware of all risks associated within and around the segregated areas;
• Whether the designated plots for containing hazardous substances are sited on impervious ground with an adequate drainage slope, (1 in 40 to 1 in 60);
• Whether mixing of incompatible substance can occur within the drainage system or anywhere that leaks/spills may accumulate (in particular consideration of the location and routing of pipelines/pumps etc from which hazardous substances may leak);
• Whether the processes and plant operating procedures minimise the inventories of hazardous substances stored, handled or in process;
• Whether plots containing flammable and toxic chemicals are sufficiently ventilated;
• Whether enclosed plots containing flammable chemicals have sufficient explosive relief systems within the building structure to allow for safe relief ventilation;
• Whether the bund facilities are sufficient to contain a maximum volume of spillage from a hazardous chemical storage vessel;
• Whether there are sufficient emergency provisions in place to control the risks associated with leaks and spills (fire extinguishers/blankets/hydrants, absorbent materials, PPE/RPE, emergency services, emergency evacuation procedures); and
• Whether there are sufficient escape routes in place in the event of a major accident or hazard (minimum of two escape routes, no dead end should exceed 8 metres).

Major hazards

Major hazards could arise from the following:

• Storing incompatible substances together;
• Domino effects (e.g. thermal radiation from fires);
• Direction of leaks to common sumps/manifolds;
• Incorrect labelling/delivery of raw materials, intermediates and products;
• Introduction of ignition sources into segregated areas containing flammable, combustible and explosive substances (e.g. smoking, mobile equipment and vehicles, power tools);
• Use of non-intrinsically safe equipment within intrinsically safe zones;
• Poorly managed inventory control and identification systems for hazardous chemicals stored in drums and vessels;
• Poor house keeping.

Codes of Practice and guidance relating to the Segregation of hazardous materials

The following publications can be used as guidance material relating to segregation of hazardous materials:

• LPGA Code of Practice 1. Bulk LPG Storage at Fixed Installations (Part 1, Part 2, Part 3 and Part 4), LP Gas Association.
  Supersedes HS(G)34 Storage of LPG at fixed installations, HSE, 1987.
  Part 3, Section 2 gives guidance on plant location and safety distances. Table 1 provides separation distances from buildings, boundaries and sources of ignition. Table 2 provides separation distances from other flammable liquids depending upon vessel size and flammable liquid flash point. Table 3 provides separation distances from liquid oxygen storage.
• HS(G)34 Storage of LPG at fixed installations, HSE, 1987.
  Superseded by the above.
  Paragraph 25 refers to the segregation of LPG vessels from bund walls designed to contain flammable substances. Table 3 summarises the minimum separation distances of LPG vessels from flammable substance's vessels and bunds, depending on their flashpoints.
  Paragraph 26 refers to a minimum separation distance of 15m between LPG vessels and toxic/hazardous substances stored under pressure. Table 4 summarises the separation distances of LPG vessels and liquid oxygen depending on their volume capacities.
  Paragraphs 28-32 refers to the criteria for segregation of LPG vessels from each other and LPG cylinders depending on number of storage vessels and the type of LPG cylinders.
• HS(G)71 Chemical warehousing: the storage of packaged dangerous substances, HSE, 1998.
  This document provides general guidance on measures on the design, construction, operation and maintenance of storage areas and buildings used for storing packaged dangerous substances.
  Paragraphs 29 to 34 describe the classification and labelling of dangerous goods.
  Paragraph 52 refers to the necessity of training to recognise the dangers of storing hazardous substances and how risk assessments should be used to evaluate training and retraining needs.
  Paragraphs 60 to 73 describe the measures for segregation of incompatible substances.
  Paragraphs 74 to 102 describe the building design requirements, including ventilation.
  Paragraphs 103 to 110 describe the measures for spill control.
• HS(G)176 The storage of flammable liquids in tanks, HSE, 1998.
  Paragraphs 46-55 refers to recommended segregation distances during flammable storage. It recommends that tanks stored above ground level should be not be stored near site boundaries, process operations, sources of ignition. The accessibility of the emergency services should also be taken into account. Table 3 is an example of a compact block layout system.
  Paragraph 50, Table 2 refers to the segregation of small tanks with a diameter of less than 10m. It illustrates the recommended separation distances between them depending on their diameter.
  Paragraph 52, Table 3 refers to the segregation of each small tank within a group depending on the tank size.
  Paragraph 55, Table 5 refers to the segregation distance of large tanks.
• CS21 Storage and handling of organic peroxides, HSE, 1991.
  This document sets out standards for the safe handling and storage of organic peroxides.
  Paragraphs 9 to 19 set out the building design requirements.
  Paragraph 20 sets out the required minimum separation distances.
• CS3 Storage and use of sodium chlorate and other similar strong oxidants, HSE, 1998.
  Paragraph 6 refers to the need to separate sodium chlorate from flammable substances and sources of ignition. It can be stored with other compatible strong oxidising agents.
  Paragraph 7 refers to the need for sodium chlorate to be stored on concrete, brick or steel floors, which are impervious. No smoking area warning signs should be in place within these segregated areas.
• CS18 Storage and handling of ammonium nitrate, HSE, 1986.
  Paragraph 12 refers to segregation of ammonium nitrate from possible sources of heat, fire or explosion (e.g., oil storage, gas lines, timber yards, flammable substances, and combustible materials).
  Paragraph 23 refers to the need for no smoking area warning signs to be placed within these segregated areas.
  Paragraph 26 refers to the need for the local fire service to be made fully aware of the storage arrangements, the likely quantity of stored ammonium nitrate, and the local water supply.

Further reading material

• Refining Safety Code, Part 3 of Model Code of Safe Practice in the Petroleum Industry, 1981.
  This publication refers to the segregation and storage of hazardous liquids by classifying them according to their flashpoint.
• CIA Guidelines for Safe Warehousing of Substances with Hazardous Characteristics, 1990.
• FPA, Fire Safety Data: Housekeeping and General Fire Precautions, GP6, 1988
  Gives advice on the segregation of flammable liquids, gas cylinders, materials liable to spontaneous combustion and hazardous chemicals segregation.
• Basic Classification of Flammable and Combustible Liquids. Published by the National Fire Protection Association. (NFPA 321: 1987)
  This publication refers to the segregation and storage of hazardous liquids by classifying them according to their flashpoint. The classification is different to the Institute of Petroleum one by nature of the flashpoint categories.
• BS 5306 Fire extinguishing installations and equipment on premises. Part 2 : 1990 Specification for sprinkler systems.
• BS 5908 : 1990 Code for fire precautions in the chemical and allied industries.
• Robertson, R.B., 'Spacing in Chemical Plant Design against Loss of Fire', IChemE Symposium Series 47, 157, 1976.
• Sims, R.E. Jr., 'Safely Store Hazardous and Flammable Materials', Chemical Engineering 94, 13, p94 September 1987.

Case studies illustrating the importance of Segregation of hazardous materials

• Allied Colloids Limited (21/7/1992)
• B&R Hauliers (25/9/1982)
• Warehouse Fire