Hierarchy of Risk Control for Designers
CDM (GB) Knowledge Base
When designing projects with the avoidance of risk in mind designers should apply the Hierarchy of Risk Control and the General Principles of Prevention. This is a series of steps to be followed when designing to eliminate and reduce risk by their design decisions, as follows:
- Consider whether it is possible to eliminate or control the hazard and the resulting risk by designing it out, i.e. design the roof with permanent safety rails.
- Next consider whether the risk can be combated in the design i.e. change design of items to be lifted to incorporate attachment points for lifting.
- Next consider measures to control risk to all the workers i.e. design a one way system for vehicles visiting the site.
- Only as a last resort should it be necessary to control risk by means of personal protection.
The General Principles of Prevention are the same in CDM as they are within the Management of Health and Safety at Work Regulations 1999.
Should risks remain which are not reasonably practicable to avoid after the application of the above hierarchy, then information needs to be given about them. This information should be included with the design and included within the Pre-Construction Information to warn others of risks about which they cannot reasonably be expected to know.
In August 2010 the HSE re-published on their web site the red, amber and green lists. The red, amber and green lists (RAG Lists) are practical aides to designers on what to eliminate/avoid, and what to encourage. The HSE are keen to stress these are not "right" or "wrong" ideas but are a basis for a debate forum to take design safety onto the next level, and can be amended to be more specific to what a particular design organisation does.
These are examples of hazardous procedures, products and processes that should be eliminated from the project where possible.
- Lack of adequate pre-construction information, e.g. asbestos surveys, geology, obstructions, services, ground contamination, etc.;
- Hand scabbling of concrete ('stop ends', etc);
- Demolition by hand-held breakers of the top sections of concrete piles (pile cropping techniques are available);
- The specification of fragile roof-lights and roofing assemblies;
- Process giving rise to large quantities of dust (dry cutting, blasting etc.);
- On-site spraying of harmful particulates;
- The specification of structural steelwork which is not purposely designed to accommodate safety nets;
- Designing roof mounted services requiring access (for maintenance, etc.), without provision for safe access (e.g. barriers).
- Glazing that cannot be accessed safely. All glazing should be anticipated as requiring cleaning and replacement, so a safe system of access is essential;
- Entrances, floors, ramps, stairs and escalators. Etc. not specifically designed to avoid slips and trips during use and maintenance, incl. effect of rain water and spillages;
- Design of environments involving adverse lighting, noise, vibration, temperature, wetness, humidity and draughts or chemical and/or biological conditions during use and maintenance operations;
- Designs of structures that do not allow for fire containment during construction.
These are examples of products, processes or procedures to be eliminated or reduced as far as possible and only specified/allowed if unavoidable. Including amber items would always lead to the provision of information to the Principal Contractor (or contractors on a non-notifiable project).
- Internal manholes/inspection chambers in circulation areas;
- External manholes in heavy used vehicle access zones;
- The specification of "lip" details (i.e. trip hazards) at the tops of pre-cast concrete staircases;
- The specification of shallow steps (i.e. risers) in external paved areas;
- The specification of heavy building blocks i.e. those weighing >20kgs;
- Large and heavy glass panels;
- The chasing out of concrete / brick / block walls or floors for the installation of services;
- The specification of heavy lintels (the use of slim metals or hollow concrete lintels being alternatives);
- The specification of solvent-based paints and thinners, or isocyanates, particularly for use in confined areas;
- Specification of curtain wall or panel systems without provision for the tying of scaffolds;
- Specification of blockwork walls >3.5 metres high using retarded mortar mixes;
- Site traffic routes that do not allow for 'one way' systems and/or vehicular traffic segregated from site personnel;
- Site layout that does not allow for adequate room for delivery and/or storage of materials, including specific components;
- Heavy construction components which cannot be handled using mechanical lifting devices (because of access restrictions / floor loadings etc);
- On-site welding, in particular for new structures;
- Need to use large piling rigs and cranes near 'live' railways and overhead electric power lines or where proximity to obstructions prevents guarding of rigs.
There are products processes or procedures to be positively encouraged.
- Adequate access for construction vehicles to minimise reversing requirements (one-way systems and turning radii);
- Provision of adequate access and headroom for maintenance in plant rooms, and adequate provision for replacing heavy components;
- Thoughtful location of mechanical / electrical equipment, light fittings, security devices etc. to facilitate access and away from crowded areas;
- The specification of concrete products with pre-cast fixings to avoid drilling;
- Specify half board sizes for plasterboard sheets to make handling easier;
- Early installation of permanent means of access, and prefabricated staircase with hand rails;
- The provision of edge protection at permanent works where there is a foreseeable risk of falls after handover;
- Practical safe methods of window cleaning (e.g. from the inside);
- Appointment of a temporary Works Coordinator (BS 5975);
- Off-site timber treatment if PPA and CCA based preservatives are used (Boron or copper salts can be used for cut ends);
- Off site fabrication and prefabricated elements to minimise on site hazards;
- Encourage the use of engineering controls to minimise the use of Personal Protective Equipment.
This RAG List, and the List prepared for the Highways Sector, are available from: www.hse.gov.uk/construction/cdm.htm.
Other guidance for designers can be found within the following documents:
- CDM07/4 Industry Guidance for Designers
- APS – Designers guide
- CIRIA 662 – CDM2007-Construction work-sector guidance for designers
- CIRIA 663 – CDM2007-Workplace "in-use" guidance for designers
- HSE Designer section at: www.hse.gov.uk/construction/cdm/designers.htm
The designer has duties whenever he/she prepares a design and does not depend upon having a client, on planning permission being given or funds being allocated. The designer has duties even if the client is a domestic client and the project is not notifiable.