12
2 Review of Literature: Motorcycle helmet
volume; visual factors; speech and sound factors and helmet compatibility. Thermal
properties of industrial safety helmets are one of the important parameters for workers
in a tropical or subtropical climate among these 12 factors.
2.5 Cooling the Motorcycle Helmet
Generally, the cooling or ventilation system in a motorcycle helmet is minimal.
The one-inch thickness of insulation liner in the interior of the helmet restricts and
virtually eliminates heat exchange with the outside wall of the most efficient part of
the skin. This creates an uncomfortably hot environment for the head of the wearer.
The interior of the helmet can quickly rise to temperatures of 37–38 °C. When
this occurs, the physiological and psychological effects on the rider are potentially
dangerous, due to a decrease in the ability to concentrate. It has been observed that
head cooling is the most efficient of any part of the body because it has the highest
skin temperature as well as large constant-volume blood flow [16]. Head cooling has
been perceived as a necessity to provide overall thermal comfort to an individual
rider.
A rough measure of the discomfort due to the wearing of helmets can be estimated
by calculating the discomfort factor used in air conditioning [17]. The human head
is represented as two thermal compartments with the inner one as the body core and
the outer one as the skin layer. The metabolic rate and heat due to the sun on the head
are measured as 6.7 W/m
2 and 8.33 W/m
2 , respectively, which corresponds approximately to 10% of total body values. The thermal discomfort can be quantified on a
0–5 grade scale, with grade 0 as comfortable and grade 5 as highly uncomfortable.
The total energy balance of the head can be represented [18] as shown in Eq. (2.1):
Metabolic heat + heat due to sun = sensible heat loss
+ evaporative heat loss + heat stored in the body
(2.1)
The helmets generally used are either open-faced or closed-faced helmets having
the option of a visor which can be opened or closed as needed by the motorcyclist.
Some form of motorcycle helmet has been used since the early twentieth century.
Their widespread use, and ultimately their mandatory use, only developed from the
late 1950s. The Snell Foundation firmly established a standard and demonstrated
the benefits of wearing a helmet. With improved technology, the speed, power and
numbers of motorcycles have increased in the last two decades. Therefore, it is now
essential that an efficient and effective motorcycle helmet should be designed and
developed that provides both adequate protection in case of an accident and adequate
cooling to minimise the thermal stress that may compromise the performance of the
rider. These features must be designed for performance and style, so as to appeal
sufficiently to motorcyclist so that helmet use increases.
2 Review of Literature: Motorcycle helmet
volume; visual factors; speech and sound factors and helmet compatibility. Thermal
properties of industrial safety helmets are one of the important parameters for workers
in a tropical or subtropical climate among these 12 factors.
2.5 Cooling the Motorcycle Helmet
Generally, the cooling or ventilation system in a motorcycle helmet is minimal.
The one-inch thickness of insulation liner in the interior of the helmet restricts and
virtually eliminates heat exchange with the outside wall of the most efficient part of
the skin. This creates an uncomfortably hot environment for the head of the wearer.
The interior of the helmet can quickly rise to temperatures of 37–38 °C. When
this occurs, the physiological and psychological effects on the rider are potentially
dangerous, due to a decrease in the ability to concentrate. It has been observed that
head cooling is the most efficient of any part of the body because it has the highest
skin temperature as well as large constant-volume blood flow [16]. Head cooling has
been perceived as a necessity to provide overall thermal comfort to an individual
rider.
A rough measure of the discomfort due to the wearing of helmets can be estimated
by calculating the discomfort factor used in air conditioning [17]. The human head
is represented as two thermal compartments with the inner one as the body core and
the outer one as the skin layer. The metabolic rate and heat due to the sun on the head
are measured as 6.7 W/m
2 and 8.33 W/m
2 , respectively, which corresponds approximately to 10% of total body values. The thermal discomfort can be quantified on a
0–5 grade scale, with grade 0 as comfortable and grade 5 as highly uncomfortable.
The total energy balance of the head can be represented [18] as shown in Eq. (2.1):
Metabolic heat + heat due to sun = sensible heat loss
+ evaporative heat loss + heat stored in the body
(2.1)
The helmets generally used are either open-faced or closed-faced helmets having
the option of a visor which can be opened or closed as needed by the motorcyclist.
Some form of motorcycle helmet has been used since the early twentieth century.
Their widespread use, and ultimately their mandatory use, only developed from the
late 1950s. The Snell Foundation firmly established a standard and demonstrated
the benefits of wearing a helmet. With improved technology, the speed, power and
numbers of motorcycles have increased in the last two decades. Therefore, it is now
essential that an efficient and effective motorcycle helmet should be designed and
developed that provides both adequate protection in case of an accident and adequate
cooling to minimise the thermal stress that may compromise the performance of the
rider. These features must be designed for performance and style, so as to appeal
sufficiently to motorcyclist so that helmet use increases.