Offshore operators are warned about the use of composite deck gratings that are not certified to survive hydrocarbon fires.
The use of composite gratings has expanded significantly in the offshore industry in recent decades, a trend confirmed by Gard’s condition survey programme for mobile offshore units (MOUs). Even older MOUs do, from time to time, replace existing steel gratings with gratings made of a composite material.
Compared with traditional engineering materials such as steel, composite materials have some apparent advantages, e.g. they have low weight, are corrosion-resistant, require less maintenance and may also be certified as ‘fire resistant’. However, a number of state regulators have issued ‘warnings’ regarding the use of composite deck gratings in locations that may be exposed to hydrocarbon fires. It appears that some types of fire resistant composite deck gratings may, after exposure to a relatively short hydrocarbon pool fire, look undamaged but will have insufficient strength to support the dynamic load of somebody walking/running. A failing deck grating can have serious consequences, e.g. for fire fighters or members of the rescue teams involved in a fire.
Gard is concerned that some owners and operators may not be aware of the safety issues associated with some types of fire resistant composite deck gratings and that the associated risks have not been part of the decision making process for installing such gratings on walkways and stairs defined as escape and evacuation routes.
Warnings issued by state regulators
The offshore industry became concerned when an investigation by the UK Health and Executive (HSE) in 2012 demonstrated that the commonly used qualification procedures for certification of fibre reinforced plastic (FRP) gratings may not ensure their safe use onboard offshore units – where likely fire threats are hydrocarbon pool or jet fires. Experience shows that such qualification procedures are usually based on the performance requirements detailed within the US Coast Guard’s “Policy File Memorandum on the use of fiber reinforced plastic (FRP) gratings and cable trays”, but with exposure of the grating to a standardised time-temperature curve for a cellulosic fire for a period of 60 minutes only. Compared to a hydrocarbon pool fire, however, which may reach temperatures above 1,000°C after only 5-10 minutes, a standard cellulosic fire has a slow growth and will typically reach temperatures of around 900°C after one hour.
Tests carried out by the UK HSE showed that the time to failure or weakening of FRP gratings exposed to hydrocarbon fires can be substantially shorter than in standardised cellulosic fires for which most FRP gratings are certified. These tests also identified the possibility that the grating may appear to have retained its integrity post-fire, but may actually have insufficient strength to support the dynamic load of somebody walking/running.
A number of ‘official warnings’ have been published following the UK HSE investigation:
The PSA auditors also found a lack of documentation of composite gratings’ static electricity characteristics, which is important in connection with the management of ignition sources in areas with potentially explosive atmospheres. See PSA’s circular of 16 November 2015 for details.
The use of non-combustible construction materials is a basic regulatory requirement in both the maritime and offshore industries and any use of materials that do not meet these requirements must be justified, and documented, from a safety point of view. Composite gratings are generally not permitted used in areas where their failure could hinder the escape from or firefighting access to a fire. It is also a general requirement, and part of a MOU’s basic safety strategy for control of ignition sources, that equipment and materials used in areas with potentially explosive atmospheres must be of a type that is approved/certified for use in that particular hazardous area.
Prior to installation of any composite deck gratings, particularly on walkways and stairs defined as escape and evacuation routes, Gard’s Members and clients are advised to:
Care should also be taken during installation of composite gratings to avoid deficient and defective installation of the grids lead to personal injury incidents at a later date.