2.11 Heat Stress
25
A motorcycle helmet should be properly designed to provide good protection
for the rider and minimise head injuries in case of accidents. Without a helmet, an
impact with any object would lead to localised high pressure on the skull, resulting in
brain injury. While designing helmets, the functional (penetration resistance, shockabsorbing capability, retention and reliability) and non-functional (thermal characteristics, cost, weight and comfort) aspects should be taken into consideration. If the
design of a helmet is good but the non-functional aspects are not properly addressed,
riders will be unwilling to wear the helmet.
Patel and Mohan [77] in a survey of 200 riders of MTW in India observed that
72% of them did not want to wear helmets, as discomfort is caused in the tropical
atmosphere. The cause of discomfort is attributed to heat, especially in summer
conditions. Kim and Park [78] found that, although people are aware of the role
of a safety hat in head protection, they are unwilling to wear a safety hat because
of its pressure on the head, the feeling of perspiration and the lack of ventilation.
Humidity increases inside the safety hat because of an increase in perspiration in a
hot environment. Thus, it is advisable to wear a safety hat containing holes which
will assist in reducing moisture and increase ventilation. The physiological aspects
of safety helmets, which is the second most important parameter following head
protection from accidents, has drawn the attention of many researchers [79–85].
Comfort is not considered important for helmets that are worn infrequently or for
short periods such as fire-fighter helmets. People wearing motorcycle helmets often
complain of headaches. It has been suggested that the reasons for the headache are
the mechanical pressure of the headband and the high temperature inside the helmet
leading to heat stress. The rigid headband on modern helmets could restrict the flow
of blood if not comfortably adjusted, causing the headache [86].
Pinnoji et al. [18] investigated the airflow between the helmet and the head by
using the computational fluid dynamics (CFD) technique and the wind tunnel. The
air gap inside a helmet (between the head and the helmet) varied from 0 mm (approx.)
to 10 mm. In order to check the effectiveness of the CFD in simulating the airflow
in a gap of 10 mm, they used two concentric cylinders separated by 10 mm and
simulated with CFD. It was shown that the grooves of higher dimensions give higher
air velocities and, in addition, they result in higher stress in the brain if the groove
dimension exceeds a certain level.
Heat stress can be defined as the sum of all the internal and external heat factors
that cause the body to become fatigued and stressed. It is caused by a high external
temperature and a very high level of activity. Heat stress not only lowers the efficiency
of a person but also leads to severe accidents in the case of industrial workers.
In addition to this, heat stress also causes health problems and fatigue and affects
performance [87].
Heat stress is caused both by internal factors (body temperature, acclimatisation,
natural heat tolerance and metabolic heat generated by the workload) and external
factors (ambient air temperature, radiant heat, air velocity and humidity) [88]. Additional heat load, which is inherent for the wearer of a helmet in hot conditions, has
not been proven to affect health conditions [33]. However, there is some evidence
of psychomotor performance being severely affected by it [79]. Buyan et al. [89]
25
A motorcycle helmet should be properly designed to provide good protection
for the rider and minimise head injuries in case of accidents. Without a helmet, an
impact with any object would lead to localised high pressure on the skull, resulting in
brain injury. While designing helmets, the functional (penetration resistance, shockabsorbing capability, retention and reliability) and non-functional (thermal characteristics, cost, weight and comfort) aspects should be taken into consideration. If the
design of a helmet is good but the non-functional aspects are not properly addressed,
riders will be unwilling to wear the helmet.
Patel and Mohan [77] in a survey of 200 riders of MTW in India observed that
72% of them did not want to wear helmets, as discomfort is caused in the tropical
atmosphere. The cause of discomfort is attributed to heat, especially in summer
conditions. Kim and Park [78] found that, although people are aware of the role
of a safety hat in head protection, they are unwilling to wear a safety hat because
of its pressure on the head, the feeling of perspiration and the lack of ventilation.
Humidity increases inside the safety hat because of an increase in perspiration in a
hot environment. Thus, it is advisable to wear a safety hat containing holes which
will assist in reducing moisture and increase ventilation. The physiological aspects
of safety helmets, which is the second most important parameter following head
protection from accidents, has drawn the attention of many researchers [79–85].
Comfort is not considered important for helmets that are worn infrequently or for
short periods such as fire-fighter helmets. People wearing motorcycle helmets often
complain of headaches. It has been suggested that the reasons for the headache are
the mechanical pressure of the headband and the high temperature inside the helmet
leading to heat stress. The rigid headband on modern helmets could restrict the flow
of blood if not comfortably adjusted, causing the headache [86].
Pinnoji et al. [18] investigated the airflow between the helmet and the head by
using the computational fluid dynamics (CFD) technique and the wind tunnel. The
air gap inside a helmet (between the head and the helmet) varied from 0 mm (approx.)
to 10 mm. In order to check the effectiveness of the CFD in simulating the airflow
in a gap of 10 mm, they used two concentric cylinders separated by 10 mm and
simulated with CFD. It was shown that the grooves of higher dimensions give higher
air velocities and, in addition, they result in higher stress in the brain if the groove
dimension exceeds a certain level.
Heat stress can be defined as the sum of all the internal and external heat factors
that cause the body to become fatigued and stressed. It is caused by a high external
temperature and a very high level of activity. Heat stress not only lowers the efficiency
of a person but also leads to severe accidents in the case of industrial workers.
In addition to this, heat stress also causes health problems and fatigue and affects
performance [87].
Heat stress is caused both by internal factors (body temperature, acclimatisation,
natural heat tolerance and metabolic heat generated by the workload) and external
factors (ambient air temperature, radiant heat, air velocity and humidity) [88]. Additional heat load, which is inherent for the wearer of a helmet in hot conditions, has
not been proven to affect health conditions [33]. However, there is some evidence
of psychomotor performance being severely affected by it [79]. Buyan et al. [89]