In the previous in Chapter 1, the overview of this study was explained about and the problem was identified. Then from the overview, the aims of the study are to explore the challenges faced in construction site during night time, to identify the different factors associated with safety during night-time construction. Through the chapter, the elaborations of the topic are clearly described. The clarification of the sub-topic will studies about the night time construction, planning aspect, and the impact of night-time construction operations on safety, quality, environmental factors, and productivity.
2.2 Definition of Night work
According to Derek Simpson (2005), night work is defined as a 7 hour period which includes that between midnight and 5am, usually 11pm to 6am. Anyone who normally works at least 3 hours of their working day during this night period is classed as a night worker. Night workers should not work more than an average of 8 hours in every 24. Where such work involves any "special hazards or heavy physical or mental strain" the 8 hours limit applies to each 24 hour period, not an average 8 hours over the reference period.
2.3 Overview of Night-time construction
2.3.1 Planning of construction work at night
Working during night time by its very nature is dangerous. Workers are exposed to many high risk unsafe working conditions at construction site. Common problems that might occur are poor visibility in the working environment, working in a drowsy condition, and communication problems with the day shift. This could contribute to other work related safety and health problems for example drug and alcohol abuse, psychological problems, and physiological problems.
Therefore, it is very important to plan any works for night time is engaged. Employers need to plan before hand the workforce required, special arrangement for safety provision such as sufficient work area lighting, retro-reflective clothing, flashing lights on equipments or structures and retro-reflective tape at work area surroundings.
2.3.2 Factors (Parameters) affecting night time work
In order to decide when to conduct night time work, factors (parameters) affecting night time work must be identified. The following factors were identified: (Kimberly D. Douglas, 2003)
Night time construction introduces numerous risks to a construction project. One clear set of examples is driver and worker fatigue and reduced visibility, which are factors that could increase safety risks. Other major factors contributing to the risks of night time work are human factors such as sleep, stress, work, social or domestic issues, and psychological characteristics, such as appetite and safety. Additional factors associated with the risks of night time construction work zones are reduced work space for machinery and equipment movement, inadequate lighting, high speed of traffic during the night, and long working hours (12 to 14 hours). (Jennifer S. Shane, 2012)
Risk management process
The best way to address night time construction work-zone risks and hazards is through risk management programs. It is suggested that agencies and contractors begin their risk management processes early and review the risk management program carefully prior to beginning night time work. Risk management is the term used to describe a sequence of analysis and management activities focused on identifying and creating a response to risks and, in the case of night time construction, to project-specific risks. Various organizations use very similar steps, but slightly different terms, to describe their risk management approach. These are the important risk management steps:
1. Risk identification.
2. Risk assessment/analysis.
3. Risk mitigation and planning.
4. Risk allocation.
5. Risk monitoring and control.
Risk identification is the process of determining which risks might affect the project and documenting their characteristics using tools such as brainstorming and checklists.
Risk assessment/analysis involves the quantitative or qualitative analysis that assesses impact and probability of risk.
Risk mitigation and planning involves analyzing risk response options (acceptance, avoidance, mitigation, or transference) and deciding how to approach and plan risk management activities.
Risk allocation involves placing responsibility for a risk on a specific party or parties typically through a contract. The fundamental tenets of risk allocation include allocating risks to the party that is best able to manage them, allocating risks in alignment with project goals, and allocating risks to promote team alignment with customer-oriented performance goals.
Risk monitoring and control is the capture, analysis, and reporting of project performance, usually as compared to the risk management plan. Risk monitoring and control assists in tracking and resolution.
Types of Risk
The first step in an effective risk management program is to identify possible risks. Specific concerns related to night time work zones include poor visibility and work quality, staffing issues, unwanted noise and glare, decreased worker and driver alertness, impaired drivers, higher vehicle speeds, increased labour costs, materials and traffic control, and problems in logistics and supervision. These risks are categorized broadly as safety, cost/production and schedule, quality, organizational relationships, technical, construction, economic, and environmental.
Night time construction lighting arrangements have an impact on project safety, quality, cost, and productivity. One of the main reasons illumination levels have a strong impact on the other aspects of night time construction is the fact that light influences human performance and alertness.
Recommended lighting level
A major problem with night time work-zone lighting arrangements is the insufficiency of the lighting provided to perform the construction or maintenance task. The level of lighting needed for specific construction activities depends on factors related to the humans performing the activities, as well as factors relating to the task at hand and the environment in which it takes place.
For example, visual ability is a human factor that is known to vary among workers. Therefore, lighting standards assume reasonable visual abilities that are considered to be normal, while giving some allowance for variations among individuals. This assumption allows for visual standards to be based mainly on the visual requirements of the specific tasks construction activities required.
The higher the precision required in a task, the higher the level of illumination needed.
The ability to visualize an object or a target depends on the contrast between that object and the background. Highly reflective backgrounds decrease the visibility of the target or object.
The relative speed of the object/target or its observer is another factor directly affecting the level of lighting needed for the construction task.
Faster moving objects or targets necessitate higher levels of illumination.
The size of the target observed in construction tasks has an impact on the needed level of illumination for the task. The smaller the object, the higher the level of lighting needed.
The distance between the observer and the target in each task is another determining factor in setting illumination levels. Larger distances necessitate higher levels of illumination.
Table 2.1: Task-dependent visual standards
Sound is energy in motion as a pressure wave through the air produced by a vibrating body. A decibel (dB) is the basic sound level unit; it denotes a ratio of intensity to a reference sound. Most sounds that humans are capable of hearing have a decibel range of 0 to 140. Zero dB, by international agreement, corresponds to an air pressure level of 20 micro-Pascals (in other words, the agreed-upon threshold of hearing). A whisper is about 30 dB, conversational speech is about 60 dB, and 130 dB is the threshold of physical pain. Humans sense the intensity difference of one sound from another. A three-decibel change in noise level is a barely noticeable difference, while a 10-dB change is perceived subjectively as a doubling/halving in loudness.
Noise can seriously harm human health and interfere with people's daily activities at school, at work, at home and during leisure time. According to World Health Organization (WHO) (2004), the main health risks of noise identified are:
Pain and hearing fatigue
Hearing impairment including tinnitus
Interferences with social behaviour (aggressiveness, protest and helplessness)
Interference with speech communication
Sleep disturbance and all its consequences on a long and short term basis
Hormonal responses (stress hormones) and their possible consequences on human metabolism (nutrition) and immune system
Performance at work and school
Critical health effect
Sound level dB(A)*
Outdoor living areas
Disturbance of communication
Industrial, commercial and traffic areas
Music through earphones
Ceremonies and entertainment
Table 2.2: WHO Community Noise Guidance
According to Dennis H. Shreve (1994), vibration can be defined as simply the cyclic or oscillating motion of a machine or machine component from its position of rest.
Many types of construction activities cause vibrations that spread through the ground (ground-borne), most notably pile driving, hoe ram demolition, blasting, and vibratory compacting. Though the vibrations diminish in strength with distance from the source, they can produce annoying or objectionable audible and "feel able" levels in buildings very close to construction sites.
Rarely do vibrations reach levels that cause structural damage to buildings. However, minor cosmetic damages can occur at lower vibration levels and, in the case of old, fragile, or historical buildings, a danger of significant structural damage always exists.
During the night, many households leave their windows open to take advantage of the cool night air. With urban night time construction projects being very close to people's living space, dust can be a problem.
Night time construction dust problems are accentuated by the lighting, which makes the particulate matter very visible. Fugitive dust may be generated by construction operations, and the contract specifications should require that the contractor prepare a dust control plan. In many cases, dust control is not a problem that is limited to night time activities; therefore, air quality or dust control plans should be for all hours of the day or night.