Calculating Relaxation Allowances

Relaxation allowances are normally applied individually to the basic time of each work element. The resulting standard element times are combined to produce standard times for complete operations. Most relaxation allowances fall into the categories of either ‘fixed allowances’ or ‘variable allowances’.

Fixed Allowances

Fixed allowances take into account the operative’s ‘personal needs’ and ‘basic fatigue’, and are considered a minimum requirement. The personal needs allowance is applied to every task and enables the worker to attend to activities such as washing or drinking – a typical value is 6% of basic time. The basic fatigue allowance is the minimum value required to accommodate moderate energy expenditure and to alleviate monotony; a typical value is 4% for a worker who is seated and engaged on light work with normal movements in good working conditions. The majority of tasks in the construction industry are usually allocated a fixed allowance of 10% of basic time, with only a few requiring more than 17%.

Variable Allowances

Fixed allowances are not sufficient to protect the long and short-term health of the worker. This problem is overcome by supplementing the fixed allowance with a ‘variable allowance’, comprising: ‘additional fatigue allowances’ where additional inputs of physical or mental work arise; and ‘environmental allowances’ to account for any adverse working conditions. Additional fatigue allowances are applied on an elemental basis, whereas environmental allowances are usually applied on a daily basis. A traditional method of calculating standard times for a typical concreting operation is presented in Table 1. The relaxation allowances applied in this example are based on values recommended by the Local Authorities Management

Services and Computer Committee (LAMSAC, 1971). The total relaxation allowance comprises factors for the following:

(a) Basic allowance

(b) Standing or sitting allowance

(c) Posture and movement

(d) Energy output.

When traditional systems for determining relaxation allowances are compared with classic ergonomics theories, several inconsistencies occur. These inconsistencies stem from either the method used to build up relaxation allowances or their subsequent application. Most discrepancies resulting from the build-up of relaxation allowances arise because the calculations are performed on an elemental basis.

For example: the personal needs factor represents a minimum period of time and should not be applied to individual elements but to complete operations; no account is taken of the opportunity to recover during waiting periods or whilst performing elements requiring little effort; the effort factor does not take into account which part of the body is being used or the number of times an operation is performed; and allowances are sometimes included for factors that do not contribute to overall fatigue.

The majority of manufacturing operations involve elements of work that require similar levels of effort with very few interruptions, and as a result these discrepancies have little or no effect. In contrast, construction operations often involve work elements requiring considerably different levels of effort with regular interruptions; consequently, these discrepancies cannot be ignored. It is for this reason that a detailed investigation was performed to establish a more theoretical valid system for determining construction relaxation allowances.

An improved system for determining construction relaxation allowances

At this stage it is important to emphasise that relaxation allowances are applied to ensure that the worker has time to attend to personal needs, whilst ensuring ability to recover from the metabolic, mental and postural cost of the work. The discrepancies discussed previously arise because these two types of allowances are combined on an elemental basis. For this reason, ‘basic allowances’ are now treated as a minimum level of relaxation; with ‘health and safety’ allowances accounting for mental cost, environmental costs, metabolic cost and local muscle fatigue, as summarised below.

Mental cost (concentration or boredom)

Some tasks require minimal muscular activity or energy expenditure but can still cause some fatigue (for example, mental tiredness). The construction operations under consideration are predominantly physical; therefore, a detailed investigation into relaxation allowances for mental fatigue is not required.

Environmental cost

Environmental allowances are used to account for abnormal working conditions resulting from the effect of weather, dust, fumes or noise. Basic allowances are often increased to accommodate any adverse environmental conditions.

Metabolic cost

Large loads applied to the body as a whole over a period of time cause a debit from the metabolic store, and relaxation periods are required to replenish it. Local muscle fatigue Local muscle fatigue occurs with little metabolic costs when either poor postures are adopted or small loads are consistently applied to the same groups of muscles. Local muscle fatigue can be either static or dynamic depending upon the frequency of loading.

Relaxation allowances for the metabolic cost of work

When loads are applied to the body as a whole, it is possible to determine the metabolic cost in terms of energy output by measuring the oxygen consumption over a period of time (Astrand, 1960). Previous research has shown that over an 8-h working day an acceptable work level is approximately equivalent to a third of the maximum oxygen intake rate (VO2 per hour)

(Legg and Myles, 1981 ; Deivanayagam and Ayoub, 1979; Lehmann, 1958; Murrell,