BARK PIT A construction made to retain loose fill materials.

BULK DENSITY The mass of material per unit volume.

CONIFER Cone-bearing tree species, including pines, spruces, larches, firs, hemlock etc..

CRITICAL FALL HEIGHT The maximum height of fall from the play equipment onto the ground or impact absorbing surface, without sustaining serious injury.

FINES A term referring to the fine particle fraction of a growing medium or mulch.

FREE HEIGHT OF FALL Distance from the clearly intended body support to the impact area.

GEO-TEXTILE SEPARATORS A sheet, usually pervious, which is used when installing a 'bark pit', to keep the LIAS material separate from the sub-base. As this sheet is pervious, it allows any rain water to drain away.

GRANULAR BARK A term used to describe the quality of bark from pine trees.

HARDWOOD Broadleafed tree species including Oak, Beech, Ash, Sycamore etc.

HEAD FORM A piece of laboratory equipment which represents a child's head and is used when carrying out tests on impact absorbing surfaces.

HEAD INJURY CRITERIA The method of assessing the height from which a child could reasonably safelt fall from the equipment onto an impact surface.

LIAS The common abbreviation for Loose Impact Absorbing Surfaces.

LOOSE IMPACT ABSORBING SURFACE The term to describe 'loose-fill' play surfaces, such as bark, wood, sand and gravel materials.

NOMINAL PARTICLE SIZE The term used to describe the physical partical size range, in millimetres, of mulches, soil ameliorants and composts. By the nature of these products, exact sizes are not possible.

NPFA An independent national body concerned with playgrounds and playing fields. The offer technical advice and an inspection service.

PLAY VALUE The term used to describe the interaction between the playground, the play equipment and the child using the facility.

ROSPA An independent national body concerned with the prevention of accidents. They have a section dedicated to play, with technical experts located throughout the UK.

RUBBER TILES Factory made rubber tiles that are used as an impact absorbing surcage, in conjunction with outdoor play equipment.

SETTLEMENT The gradual sinking and reduction in volume exhibited by loose fill materials, such as bark mulches or play surfaces, mostly occuring soon after installation. When calculating the quantity of product needed for an area, to acheive the required finishing depth, it is important to consider the amount of settlement which will occur with the chosen product. In general, products manufactured from the softer, thinner barks such as spruce will settle more than the harder ones such as pine.

SPRUCE BARK The bark of spruce trees is flexible, dark brown to black in colour, stringy rather than chippy, and much softer than pine bark. It is less durable than pine, breaking down more quickly, and it can therefore form a very useful basis for soil improvement products.

TOP UP If products manufactured from bark are to remain effective in any given situation, it is important that their depth is maintained. Being organic in origin, bark will gradually breakdown, the rate depending very much on the species mix, the particle size and the level of wear. Once the recommended depth is significantly reduced, it is important that the level or bark is topped up in order to maintain effectiveness.

WET POUR RUBBER A rubber based material used as an impact absorbing surface, in conjunction with outdoor play equipment. The product is mixed on-site and poured in liquid form onto a prepared base.