The Lean manufacturing concept was introduced in Japan. The Toyota company first implemented the concept and was known as Toyota Production System. However, nowadays, the Lean concept is widely applied in industries. Lean manufacturing is defined as providing quality products while maintaining the low cost of manufacturing. The primary purpose of Lean manufacturing is to minimize enterprise waste, as waste is an extra resource burden that never adds value to the company. Lean manufacturing tools minimize operational costs by reducing waste, optimizing product quality, and increasing efficiency [1]. Furthermore, the Lean manufacturing concept is one of the most popular and widely used methods in the industries to achieve maximum productivity, high quality, and cost reduction in organizations. Results of a study concluded that the Lean concept boosts the productivity of organizations, reduces the cost of manufacturing, eliminates unnecessary downtime, better the utilization of resources, and maximizes profitability. Therefore, the Lean concept enhances the competitiveness of any organization in the market [2]. Therefore, enterprises strive to adopt the Lean manufacturing concept to become economically sound and practical. It was seen that there was a continuous improvement in organizations after the application of the Lean manufacturing concept [3]. The introduction of Lean manufacturing tools such as Total Productive Management (TPM), overall equipment effectiveness (OEE), and Jidoka directly impact the environment of the enterprise, social, and economic sustainability. Therefore, a safe working environment is the cause of improvement in employee commitment, morale, safety, and delivery time [4].
Lean manufacturing has operational benefits regarding quality, delivery, cost, and volume flexibility. It was shown that adopting digital technology and Lean manufacturing reduces production costs despite the different environmental conditions. The application of Lean manufacturing together with digital technology improves operational performance and efficiency of production management. Lean implementation has been shown to improve the financial standing of an enterprise by maintaining a safe shop floor management approach [5]. The introduction of the Lean manufacturing concept in the management of railway transport enterprises results in the optimization of labor and material resources. Thus, it helped reduce operation time, generate a safe environment for labor, improve transportation quality, and expand their customer base [6].
Back in 1970 5S method was first introduced by Takashi Osada [7] to sustain the implementation of the Lean concept. 5S, a Lean tool, includes elements such as Sort, Set, Shine, Standardize and Sustain. The Safety was later added to make the 5S+1. These tools eliminate unnecessary items that do not add value to the production by fixing an unhealthy, untidy work environment. In a study, ten different manufacturing units were used to find out the effect of the use of 5S, and it showed a positive result on the manufacturing units. Furthermore, after applying 5S, there was a continuous improvement in the workplace and clear evidence of improvement in employee human relations and motivation [8]. 5S system is the first step into Lean thinking to minimize waste and maximize productivity. Through it, they maintain discipline and order in workstations hence efficient and effective operational results [9]. Therefore, the 5S can be considered to be a cyclic method. As a result, there is a continuous improvement [10]. Even when applied in a limited resources environment, 5S has proven to bring positive changes in the work environment of health centers by reducing the number of unwanted items, improved directional indicators, and labeling the units of service. Thus, increasing the quality of services in a more efficient, safe, and patient-centered style also helped improve the behaviors of staff and patients towards the resources of the workplace [11]. Applying the 5S in a medical laboratory brought a higher order level, helped eliminate unnecessary objects, and increased productivity [12]. It was found that applying 5S in hospitals eliminated waste in motion, thus helping to reduce cycle time [13]. Consequently, a more Lean and more organized work environment was created while controlling work accidents and errors beforehand [14]. The application of 5S in the fast food industry contributed to optimizing the work process. It also contributed to a decrease in production time; and a reduction in energy consumption [15]. Implementing 5S has been shown to improve safety, minimize defect rates, increase equipment availability [16], and better cost reduction, which can result in higher agility and flexibility of the manufacturing enterprise and positively impact employee morale [17]. Applying the 5S methodology in packaging improved quality and food safety [18]. Furthermore, applying 5S in restaurant management caused a reduction in the number of steps that need to be taken by employees to fulfill a specific task. It also helped reduce the time spent searching for materials by 95%. Thus, helping reduce order time, serving more customers, and making more profits [19]. The use of 5S positively impacts performance by enhancing manufacturing production quality and effectiveness [20]. 5S+1 has also been used to organize the workplace at a scientific instruments manufacturing company [21] and achieved results in process improvement, continuous improvement, and waste reduction [22].
1.1 Sort in 5S+1
This is the first step when implementing the 5S+1 strategy. It improves the quality of the work with better care in keeping things in order, thus improving the management of the workspace. Sort helps separate waste from the manufacturing process [23]. The first S, Sort, eliminates steps that do not add value [24]. In this process, a red tag is placed on the unnecessary items or the items that are not in the proper place or quantity. The red tag items are then moved or recycled, disposed or reassigned. Hence sorting helps to generate floor space and remove the items that are broken, scrap, or excess raw material [25]. The Sort element of 5S helps enterprises shorten searching time, maintain a Lean and safe workspace and quickly detect any fault in equipment [26]. The 5S method is a foundation for improving the production process in any company. That is why it should be adequately implemented to increase the effectiveness of a process by eliminating waste [27].[28].
1.2 Shine in 5S+1
Once sorting is done, keeping order in the workspace is vital. Routine Lean up is essential for the production system's proper functioning. In 5S+1, work is divided among employees in terms of the Leaning time and area of Leaning [29]. Also, faulty equipment due to excessive vibrations, leakages, misalignments, and other causes can be easily noticed in a Lean working environment. If these malfunctions are not fixed at the moment, it can lead to loss of production or equipment failure. Therefore, having a Lean and organized workplace can help prevent sources of potential failure or downtime from going unnoticed. Shine is taken from Seiso, which means sweep, scrub, or shine. The primary purpose of Seiso is to Lean up the workspace by removing dust, dirt, chips, and other contaminations. It emphasizes on that by guiding operators or workers on the shop floor to maintain the state of Lean of the machines and shop floor. Training is given to the employees about the adverse effects of contamination and how to avoid them to establish and maintain a risk-free working environment [30]. Shine indicates the need to Lean systematically to keep a healthy work environment, which helps maintain quality work in production [31]. When equipment is Lean, it performs more efficiently, thus eliminating extra costs that can be incurred due to unnoticed problems. Manufacturers have realized that if machines are kept clean while daily maintenance is carried out, chances of downtime decrease; thus, margins of profits increase [32]. It has been documented that the number of common accidents and risks in a Lean factory has gone down in a Lean workspace or shop floor [33].
1.3 Set in 5S+1
Set or Seiton is another element of the 5S+1 method that means systemization, set in order, or organization. It helps in a facility layout when planning where to place different resources such as raw materials, machine tools, semi-finished products, etc. This strategy ensures that it should not take more than 30 seconds to find a necessary object [23]. Once the sort has eliminated all the unnecessary items, set in order can be implemented. Set in order means to arrange items based on size and frequency of use. Further, the items are labeled for ease of use and stored or placed in a location based on that. In set in order, arrangements are made in such an order that tools are located according to the frequency of their use. As a result, this procedure helps to minimize movements and search time. Set in order can be achieved by labels, using tapes, signs, and marking floors. In addition, Seiton eliminates wastes, including search wastes, waste in motion, and excessive inventory waste [34]. Many positive changes have been noticed as a result of adopting 5S+1. For example, it was found that there was a reduction of employee movement by 60% and a reduction of 20% in operational costs [35]. Furthermore. It has been shown to increase productivity, quality of work and products, safety, health, and efficiency [36]; and reduction of waste in motion, such as excessive movements between production halls and work stations [37].
1.4 Standardize in 5S+1
Seiketsu is another element of 5S that means standardization, tidiness, and sanitization. It helps to carry out repeated activities without any hindrance and extra usage of time [23]. The primary objective of standardization is to make the first 3S; sort, set in order, and shine as a habit, so workers do not return to the old unorganized practices [38]. Seiketsu creates standards and monitors them for upcoming events, such as inspection and safety plans. Standardization aims to maintain a safe working environment and reduce the disruption that might happen due to a change in the scope of duties for the workers, allowing a shorter training time and smooth and quick adaptation to the new changes in the working environment [30]. Further, standardization prevents the accumulation of waste, and maintains a consistent procedure and a Lean working environment. Without any standards in an organization, it is impossible to improve product quality [39]. In the current overlapped environments of Lean Industry 4.0, standardization is one of the critical parameters to maintain a safe workspace, reduce disruptions, and increase production. 5S+1 is a business or industrial approach that primarily focuses on improving the production process by enhancing workplace standards [40]. In addition to integrating standards into maintenance procedures, production planning and specifications, and transportation of goods, standardization is also used in other significant activities, such as human resource management, customer service, and bookkeeping [41]. Implementation of 5S+1 depends upon employee commitment, sustainability initiatives, and training [42]. 5S+1 practices generate new rules for production plants and set up processes that are adapted in the company [43]. Chiarini [44] attempted to create a first guideline on how the 5S+1 concept and tools could be integrated into established standard texts such as ISO 9001.
1.5 Sustain in 5S+1
The Shitsuke element of the 5S means sustains. The main objective of Shitsuke is to keep or maintain all the new and effective processes as standards of the organization. Workplace inspections should be carried out as planned routine activities every specific period [23]. 5S+1 helps eliminate obstacles that reduce the potential to reach an efficient production process [45]. Sustain is viewed as an essential step to maintain the first 4S when applied while allowing for better implementation of the sixth S in safety [46]. The most crucial goal of sustain is to make the best practices a habit of the workforce in any business. Further sustain helps improve human relationships in the company as it teaches discipline and helps continuous running of the 5S+1 process [39]. Adopting 5S+1 has encouraged employees to create better work conditions by teaching them how to reduce waste through Value Stream Mapping (VSM) and continuous improvement. When implemented, the 5S+1 method influences individual behaviors. It creates simple, precise, and efficient rules, thus constructing a disciplined functional working environment [47]. It is difficult to change the traditional way of doing things and maintain the new procedures which disrupted the old ways; that is why this fifth S is considered to be the most challenging procedure [48]. Without sustain, it is impossible to maintain the application of 5S+1 [49]. Maintaining the 5S+1 strategies in the workplace simplifies the work environment and makes it easy for everyone to follow the rules and guidelines [50].
1.6 Safety in 5S+1
Safety focuses on preventive measures to protect workers from hazardous conditions and provide them with a safe environment. Studies recall that safety plays a significant role in maintaining an environment that is free of stress, safe, and secure hence improving the work environment [51].
Operations such as welding, gas cutting, and casting process need extra precautionary measures to reduce the number of incidents that can happen [52]. The 5S+1 method cannot be separated from industrial, manufacturing, or construction operations. Implementing 5S+1 tools creates safer work conditions [53], [54]. Deploying 5S+1 in the healthcare industry reduced waste and mistakes and increased productivity [55]. Applying 5S+1 ensured that operators used Personal Protective Equipment (PPE) and gear to avoid accidents. [56]. The 5S+1 method is a powerful engine that enhances the quality of the work environment by improving safety [57].