1         Legislation (regulation, directives, Specs, Papers, reports)

1.1       EU Directive 89/391/ EEC:

1.1.1     Title: .

On the introduction of measures to encourage improvements in the safety and health of workers

1.1.2     Highlights:

The object of this Directive is to introduce measures to encourage improvements in the safety and health of workers at work .

This Directive shall apply to all sectors of activity, both public and private (industrial, agricultural, commercial, administrative, service, educational, cultural , leisure, etc.).

This Directive shall not be applicable where characteristics peculiar to certain specific public service activities , such as the armed forces or the police, or to certain specific activities in the civil protection services inevitably conflict with it.

Member States shall take the necessary steps to ensure that employers, workers and workers' representatives are subject to the legal provisions necessary for the implementation of this Directive.

The employer shall have a duty to ensure the safety and health of workers in every aspect related to the work.

 

1.1.3     Comments

This directive refers to safety and health of workers at work and contains general obligations for employers and workers.

1.2       EU Directive 2002/44/EC

1.2.1     Title: .

On the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (vibration) (sixteenth individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC).

1.2.2     Highlights:

This Directive lays down minimum requirements for the protection of workers from risks to their health and safety arising or likely to arise from exposure to mechanical vibration

it is considered necessary to introduce measures protecting workers from the risks arising from vibrations owing to their effects on the health and safety of workers, in particular muscular/bone structure, neurological and vascular disorders. These measures are intended not only to ensure the health and safety of each worker on an individual basis, but also to create a minimum basis of protection for all Community workers in order to avoid possible distortions of competition.

For whole-body vibration limits are:

a)    the daily exposure limit value standardised to an eight-hour reference period shall be 1,15 m/s2 or, at the choice of the Member State concerned, a vibration dose value of 21 m/s1,75;

b)    The daily exposure action value standardised to an eight hour reference period shall be 0,5 m/s2 or, at the choice of the Member State concerned, a vibration dose value of 9,1 m/s1,75.

In compliance with the general principles of health and safety protection for workers, Member States may, in the case of sea and air transport, derogate from specified limits in duly justified circumstances with respect to whole-body vibration where, given the state of the art and the specific characteristics of workplaces, it is not possible to comply with the exposure limit value despite the technical and/or organisation measures taken.

The assessment of the level of exposure to vibration is based on the calculation of daily exposure expressed as equivalent continuous acceleration over an eight-hour period, calculated as the highest (rms) value, or the highest vibration dose value (VDV) of the frequency-weighted accelerations, determined on three orthogonal axes in accordance to ISO standard 2631-1(1997)

1.2.3     Comments

This directive is an extension of EU Directive 89/391/ EEC defining the vibration limits in accordance to ISO 2631-1.

For the sea applications, the whole body vibration limits can be considered as the most applicable.

These limits are too strict and general, making them too difficult to be implemented in a real sea wavy environment. Alternatively, the vibrations can be minimized at a lower workable level. The better the absorbing system the lower the risk for the passenger.

1.3       ISO 2631-1

1.3.1     Title: .

Mechanical vibration and shock-Evaluation of human exposure to whole body vibration-General requirements.

1.3.2     Highlights

This part of ISO 2631 defines methods for the measurement of periodic, random and transient whole-body vibration. It indicates the principal factors that combine to determine the degree to which a vibration exposure will be acceptable. Informative annexes indicate current opinion and provide guidance on the possible effects of vibration on health, comfort and perception and motion sickness. The frequency range considered is:

a)    0,5 Hz to 80 Hz for health, comfort and perception, and

b)    0,1 Hz to 0,5 Hz for motion sickness.

This part of ISO 2631 incorporate methods of averaging vibration over time and over frequency bands. The vibration evaluation always includes measurements of the weighted rms acceleration.

 

1.3.3     Comments

The ISO 2631-1 standard defines how to measure, organize and present the vibrations for evaluating the results for health, comfort-perception and motion sickness but it does not defines limits.

This method can be used to compare different seats.

This method has been adopted by EU Directive 2002/44/EC for measuring vibrations in general.

 

1.4       ISO 2631-5

1.4.1     Title: .

Mechanical vibration and shock-Evaluation of human exposure to whole body vibration- Method for evaluation of vibration containing multiple shocks.

1.4.2     Highlights

This part of ISO 2631 addresses human exposure to mechanical multiple shocks measured at the seat pad when a person is seated.

This guidance applies to people in normal health who are regularly exposed to vibration containing multiple shocks. Individuals with previous disorders affecting the spine, including those suffering from latent osteoporosis or other spinal disorders, may be more susceptible to injury. The guidance in this part of ISO 2631 applies to rectilinear x-, y- and z-basicentric axes of the human body. It does not apply to high magnitude single-event shocks such as may result from a traffic accident that causes trauma.

It is assumed that multiple shocks cause transient pressure changes at the lumbar vertebral endplates that over time may result in adverse health effects, arising from material fatigue processes. Essential exposure related factors are the number and magnitudes of peak compression in the spine. The peak compression in the spine is affected by anthropometric data (body mass, size of endplates) and posture.

Adverse health effects of long-term whole-body multiple-shock exposure includes an increased risk to the lower lumbar spine and the connected nervous system of the segments affected. Excessive mechanical stress and/or disturbances of the nutrition of and diffusion to the disc tissue may contribute to the degenerative processes in the lumbar segments. Multiple-shock and vibration exposure may also worsen certain endogenous pathological disturbances of the spine.

For the evaluation of the effects of internal pressure changes, the Palmgren-Miner approach is applied. Experimental data show that the value of the Palmgren-Miner exponent varies with biological tissue and test methodology from 5 to 14 for cortical and trabecular bone to 20 for cartilage. For the purpose of estimating adverse health effects, a conservative exponent of 6 has been selected here.

The relationship between the predicted pressure changes and the predicted total tolerance of the exposed person can be used to assess the potential of an adverse health effect. The predicted response is of the bony vertebral endplate (hard tissue). The assessment is based on upright posture. A bending forward or twisting posture is likely to increase the adverse health effect.

In general, a factor R can be defined for use in the assessment of the adverse health effects related to the human response acceleration dose. R should be calculated sequentially taking into account increased age (and reduced strength) as the exposure time increases.

R < 0,8 indicates a low probability of an adverse health effect; R > 1,2 indicates a high probability of an adverse health effect.

1.4.3     Comments

This standard is meant to be the most efficient method for such evaluations, that concern not only HSC, in respect to NATO (RTO – MP – AVT – 110) “Shock Mitigation for the Human on High Speed Craft: Development of an Impact Injury Design Rule” Report. It is chosen from many design rules, such as Root – Mean – Square (RMS), ISO® 2631 – Part 1 (1985), Dynamic Response Index Statistics (DRI), Onset – Rate Statistics and Power Spectral Density (Bandwidth – Limited) rules.

According to two more other references [(1) Paper: Prediction of Injury Risk for Occupants of HSC planning - University of Virginia, (2) IRCOBI Conference - Prague - September 2005: The modeling and measurement of humans in high speed planning boats under repeated vertical impacts] the repeated impact standard ISO 2631 Part 5 for seated occupants has been found to be as good as or better than any of the other injury criteria for application to the assessment of injury criteria in high speed planning craft.

 

1.5       IMO HSC 2000 Code

1.5.1     Title: .

International Code of Safety for High-Speed Craft

1.5.2     Highlights

The safety philosophy of this Code is based on the management and reduction of risk as well as the traditional philosophy of passive protection in the event of an accident. Management of risk through accommodation arrangement, active safety systems, restricted operation, quality management and human factors engineering should be considered in evaluating safety equivalent to current conventions. Application of mathematical analysis should be encouraged to assess risk and determine the validity of safety measures.

To clearly distinguish such craft, criteria based on speed and volumetric Froude number have been used to delineate those craft to which this Code applies from other, more conventional, craft.

This Code shall be applied as a complete set of comprehensive requirements. It contains requirements for the design and construction of high-speed craft engaged on international voyages, the equipment which shall be provided and the conditions for their operation and maintenance. The basic aim of the Code is to set levels of safety which are equivalent to those of conventional ships required by the International Convention for the Safety of Life at Sea, 1974, as amended, (SOLAS Convention) and the International Convention on Load Lines, 1966, (Load Line Convention) by the application of constructional and equipment standards in conjunction with strict operational controls.

Annex 10 - Criteria for testing and evaluation of seats: The purpose of these criteria is to provide requirements for revenue and crew seats, seat anchorage and seat accessories and their installation to minimize occupant injury and/or disruption of egress/ingress if the craft suffers a collision.

1.5.3     Comments

The Annex 10, contains criteria for static and dynamic tests of HSC seats concerning occupant injury and/or disruption of egress/ingress if the craft suffers a collision.

1.6       Other Directive

Per country or organization, there are directives which defines extra rules/limits that they should be followed by boat builders or seat manufacturers like Marine Guidance Note MGN 436 by Maritime and Coastguard Agency (MCA).

1.7       Comments

All manufactures should indicate vibration emission levels of their products.

All employers shall assess and, if necessary, measure the levels of mechanical vibration to which workers are exposed.

In any event, workers shall not be exposed above the exposure limit value.

If, despite the measures taken by the employer to comply with this Directive, the exposure limit value is exceeded, the employer shall take immediate action to reduce exposure below the exposure limit value. He shall identify the reasons why the exposure limit value has been exceeded, and shall amend the protection and prevention measures accordingly in order to prevent it being exceeded again.

Current research suggests that there is no definitive design of craft or seating which is guaranteed to mitigate all the effects of whole body vibration (WBV). There are, however, some basic principles which if followed may assist in reducing the effects of whole body vibration and in particular the impact of the craft slamming.