PERSONAL HEAD PROTECTION
Isabelle Balty and Alain Mayer
Head injuries are fairly common in industry and account for 3 to 6% of all industrial injuries in industrialized countries. They are often severe and result in an average lost time of about three weeks. The injuries sustained are generally the result of blows caused by the impact of angular objects such as tools or bolts falling from a height of several metres; in other cases, workers may strike their heads in a fall to a floor or suffer a collision between some fixed object and their heads.
A number of different types of injury have been recorded
Understanding the physical parameters that account for these various types of injury is difficult, although of fundamental importance, and there is considerable disagreement in the extensive literature published on this subject. Some specialists consider that the force involved is the principal factor to be considered, while others claim that it is a matter of energy, or of the quantity of movement; further opinions relate the brain injury to acceleration, to acceleration rate, or to a specific shock index such as HIC, GSI, WSTC. In most cases, each one of these factors is likely to be involved to a greater or lesser extent. It may be concluded that our knowledge of the mechanisms of shocks to the head is still only partial and controversial. The shock tolerance of the head is determined by means of experimentation on cadavers or on animals, and it is not easy to extrapolate these values to a living human subject.
On the basis of the results of analyses of accidents sustained by building workers wearing safety helmets, however, it seems that head injuries due to shocks occur when the quantity of energy involved in the shock is in excess of about 100 J.
Other types of injuries are less frequent but should not be overlooked. They include burns resulting from splashes of hot or corrosive liquids or molten material, or electrical shocks resulting from accidental contact of the head with exposed conductive parts.
The chief purpose of a safety helmet is to protect the head of the wearer against hazards, mechanical shocks. It may in addition provide protection against other for example, mechanical, thermal and electrical.
A safety helmet should fulfil the following requirements in order to reduce the harmful effects of shocks to the head:
Example of essential elements of safety helmet
|Other requirements may apply to helmets used for particular tasks. These include protection against splashes of molten metal in the iron and steel industry and protection against electrical shock by direct contact in the case of helmets used by electrical technicians.
Materials used in the manufacture of helmets and harnesses should retain their protective qualities over a long period of time and under all foreseeable climatic conditions, including sun, rain, heat, bela-freezing temperature, and so on. Helmets should also have a fairly good resistance to flame and should not break if dropped onto a hard surface from a height of a few metres.
ISO International Standard No. 3873-1977 was published in 1977 as a result of the work of the subcommittee dealing especially with "industrial safety helmets". This standard, approved by practically all the member states of the ISO, sets out the essential features required of a safety helmet together with the related testing methods. These tests may be divided into two groups (see table 31.7 [PPE07TE]), namely:
|The resistance to ageing of the plastic materials used in the manufacture of helmets is not specified in ISO No. 3873-1977. Such a specification should be required for helmets made out of plastic materials. A simple test consists in exposing the helmets to a high-pressure, quartz-envelope 450 watt xenon lamp over a period of 400 hours at a distance of 15 cm, followed by a check to ensure that the helmet can still withstand the appropriate penetration test.
It is recommended that helmets intended for use in the iron and steel industry be subjected to a test for resistance to splashes of molten metal. A quick way of carrying out this test is to allow 300 grams of molten metal at 1,300°C to drop onto the top of a helmet and to check that none has passed through to the interior.
The European Standard EN 397 adopted in 1995 specifies requirements and test methods for these two important characteristics.
The ideal helmet providing protection and perfect comfort in every situation has yet to be designed. Protection and comfort are indeed often conflicting requirements. As regards protection, in selecting a helmet, the hazards against which protection is required and the conditions under which the helmet will be used must be considered with specific attention to the characteristics of the available safety products.
It is advisable to choose helmets complying with the recommendations of ISO Standard No. 3873 (or its equivalent). The European Standard EN 397-1993 is used as a reference for the certification of helmets in application of the 89/686/EEC directive: equipment undergoing such certification, as is the case with almost all personal protective equipment, is submitted to a mandatory third party certification before being put onto the European market. In any case, helmets should meet the following requirements:
Helmets made of light alloys or having a brim along the sides should not be used in workplaces where there is a hazard of molten metal splashes. In such cases, the use of polyesterglass fibre, phenol textile, polycarbonateglass fibre or polycarbonate helmets is recommended.
Where there is a hazard of contact with exposed conductive parts, only helmets made of thermoplastic material should be used. They should not have ventilation holes and no metal parts such as rivets should appear on the outside of the shell.
Helmets for persons working overhead, particularly steel framework erectors, should be provided with chin straps. The straps should be about 20 mm in width and should be such that the helmet is held firmly in place at all times.
Helmets made largely of polyethene are not recommended for use at high temperatures. In such cases, polycarbonate, polycarbonateglass fibre, phenol textile, or polyesterglass fibre helmets are more suitable. The harness should be made of woven fabric. Where there is no hazard of contact with exposed conductive parts, ventilation holes in the helmet shell may be provided.
Situations where there is a crushing hazard call for helmets made of glassfibre reinforced polyester or polycarbonate having a rim with a width of not less than 15 mm.
In addition to safety, consideration should also be given to the physiological aspects of comfort for the wearer.
The helmet should be as light as possible, certainly not more than 400 grams in weight. Its harness should be flexible and permeable to liquid and should not irritate or injure the wearer; for this reason, harnesses of woven fabric are to be preferred to those made of polyethene. A full or half leather sweatband should be incorporated not only in order to provide sweat absorption but also to reduce skin irritation; it should be replaced several times during the life of the helmet for hygienic reasons. To ensure better thermal comfort, the shell should be of a light colour and have ventilation holes with a surface range of 150 to 450 mm2. Careful adjustment of the helmet to fit the wearer is necessary in order to ensure its stability and to prevent its slipping and reducing the field of vision. Various helmet shapes are available, the most common being the "cap" shape with a peak and a brim around the sides; for work in quarries and on demolition sites, the "hat" type of helmet with a wider brim provides better protection. A "skull-cap" shaped helmet without a peak or a brim is particularly suitable for persons working overhead as this pattern precludes a possible loss of balance caused by the peak or brim coming into contact with joists or girders among which the worker may have to move.
Helmets may be fitted with eye or face shields made of plastic material, metallic mesh or optical filters; hearing protectors, chin straps and nape straps to keep the helmet firmly in position; and woollen neck protectors or hoods against wind or cold (figure 31.9 [PPE09FE]). For use in mines and underground quarries, attachments for a headlamp and a cable holder are fitted.
Other types of protective headgear include those designed for protection against dirt, dust, scratches and bumps. Sometimes known as "bump caps," these are made of light plastic material or linen. For persons working near machine tools such as drills, lathes, spooling machines and so forth, where there is a risk of the hair being caught, linen caps with a net, peaked hair nets or even scarves or turbans may be used, provided that they have no exposed loose ends.
All protective headgear should be cleaned and checked regularly. If splits or cracks appear, or if a helmet shows signs of ageing or deterioration of the harness, the helmet should be discarded. Cleaning and disinfection are particularly important if the wearer sweats excessively or if more than one person share the same headgear.
Substances adhering to a helmet such as chalk, cement, glue or resin may be removed mechanically or by using an appropriate solvent that does not attack the shell material. Warm water with a detergent may be used with a hard brush.
For disinfecting headgear, articles should be dipped into a suitable disinfecting solution such as a 5% formalin solution or a sodium hypochlorite solution.
Ch. 31 Personal Protection. In Encyclopaedia of Occupational Health and Safety / edited by Janne Mager Stellman. 4th ed. Geneva : International Labour Office, 1998. Vol. 1, pt. IV.