“Man in the working environment may be exposed to the actions of various factors threatening his life and health.
From the point of view of their reaction on the human organism, these factors can be divided into: dangerous, harmful or arduous.
Depending on the concentration or dose, arduous factors may become harmful (threatening the health) or dangerous (threatening life).
According to the classification in the standards, factors from the working environment are divided into physical, chemical, biological and psychophysical depending on their nature.
Work under conditions of exposure to the action of the cited factors creates the possibility of the emergence of detrimental effects on the health or life of man, while the probability and extent that these consequences take place is defined as occupational risk…” [“Assessment of occupational risk”; – methodical foundations, ed. W. M. Zawieski]

Occupational risk, connected with the work performed, therefore, arises from the exposure of the worker to the actions of dangerous, harmful and arduous factors present at the work post.

A dangerous factor is a factor whose actions may lead to injury or other significant immediate damage to the state of human health or to a fatality.

A harmful factor means a factor whose actions may lead to a worsening of the state of human health.

An arduous factor does not actually represent a threat to human life or health, but makes work difficult or results in a significant reduction in the capacity to work or to perform other activities or reduces efficiency.

Depending on the level of reaction or other conditions, an arduous factor may become harmful and a harmful factor may become dangerous.

The performance of construction work is related to the exposure of the workers to the reaction of the majority of the above factors, creates many potential opportunities for the emergence of serious accidents at work and requires the every day adherence to occupational safety and health, regulated as a whole by the relevant legal acts.

Dangerous factors, which most frequently cause injuries, primarily include mechanical factors, such as:

•   mobile, mainly revolving, parts of machines and other devices and
    other equipment and tools
•   moving means of transport
•   sharp protruding elements
•   falling items
•   slippery and uneven surfaces
•   restricted spaces (approaches, entrances, accesses).

Dangerous factors also include electrical currents and explosions of pressurised devices (cylinders, boilers and tanks), gas pipes and installations, as well as mixtures of gases with air.  The threat of explosion may be related to the incorrect use of devices and leaks in pipes and connections, as well as incorrect operation of control and metering apparatus and security devices.

The basic requirements and measures of collective protection against potential threats, which may be caused by mechanical factors and electrical currents, have been discussed in the sections on machinery and equipment, as well as the individual construction works.

The harmful factors that could take place on the construction site include physical factors - noise, mechanical vibrations, low temperature, high humidity of the air and incorrect lighting, as well as chemical factors - wood impregnation agents, solvents, asphalt smoke and dust, including asbestos that causes asbestosis in man.

The Resolution of the Minister of Labour and Social Policy of 17 June 1998 (Journal of Laws no. 79, item 513), as amended (Journal of Laws 2002, No. 217, item 1833) specifies the values of the maximum permissible concentrations and doses of factors that are harmful to the health (MPC and MPD).  These values are obligatory for all workers, unless other detailed regulations specify lower values.

The values of MPC and MPD are the basis for implementing the planned preventive activities by employers.  The employer is obliged to conduct tests and to measure the factors that are harmful to the health at his own expense and to make these results available to the workers.

Measurements of chemical and physical factors are taken by the laboratories of:

•   the Health Inspectorate
•   research and development units in the area of occupational medicine
•   Central Institute for Labour Protection
•  laboratories that have received accreditation in accordance with the regulations on tests and certification, or which have been authorised by the voivodship health inspector

The control lists contained in this section have the objective of facilitating the identifying threats in connection with the presence of dangerous and harmful factors, and also enabling appropriate remedial action to be taken to improve the state of health and safety at work posts.

Arduous factors, which are present at construction works include: lifting and carrying loads, forced body position and stress.
The work of lifting and carrying loads is a constant activity and may be a reason for excessive physical fatigue, over-exertion of muscles, joints and most importantly, the spine.  The consequences may be emaciation of the organism, a reduction in physical efficiency, the increase in the susceptibility to accidents, emergence of tendon and spinal injuries.
The measure leading to the prevention of the detrimental effects of carrying loads is the adherence to the load carrying standards, taking into account the differences in individual fitness or that of individual groups of workers (youth, women).  In preventing the consequences of over-exertion, it is important to specify the correct methods for lifting and carrying loads at individual work posts and to train the workers on safe techniques for carrying loads.  The aim should be to reduce and eliminate manual carrying of loads, e.g. by using means of transport (trolleys, hoists).
A forced body position during the performance of work results in fast physical fatigue, reduction in work efficiency and a decrease in the speed and quality of work.  The detrimental element of this arduousness is the possibility of becoming accustomed to the wrong position at work, which after years may lead to permanent organic changes, e.g. permanent stooping, unequal development of certain muscle groups or spinal curvature.  In extreme cases, a forced position at work prevents this work from being performed for a long time (e.g. work with raised hands).
The measure for preventing the effects of forced body position is primarily the control of work posts and their optimisation using technical and organisational measures, conducted with the active participation of the workers themselves.  

Stress may result in fatigue and a reduction in mental and psychological efficiency, a reduction in immunity to diseases, a reduction in the efficiency of the sight and hearing, as well as precision in manual activities.  In consequence, it leads to an increase in the number of errors made at work, erroneous decisions, wrong assessment of the state of safety and a lack of motivation to work.  The reasons for stress include: poor work organisation, excessively fast and forced rate of work, particularly monotonous work, excessive amounts of work and poor interpersonal relationships.  
Measures that lead to a reduction in stress at work are: continuous improvement of the organisation of work, inclusion of workers in the optimisation of their own work posts, development of the attitude of commitment and positive motivation to work, team working skills and increasing the qualifications of managers in terms of methods for developing interpersonal relationships.