IHS (Intenational Hotel Management School

Reliability may be defined in several ways:

The idea that something is fit for purpose with respect to time;
The capacity of a device or system to perform as designed;
The resistance to failure of a device or system;
The ability of a device or system to perform a required function under stated conditions for a specified period of time;
The probability that a functional unit will perform its required function for a specified interval under stated conditions.
The ability of something to "fail well" (fail without catastrophic consequences)

Reliability engineers rely heavily on statistics, probability theory, and reliability theory. Many engineering techniques are used in reliability engineering, such as reliability prediction, Weibull analysis, thermal management, reliability testing and accelerated life testing. Because of the large number of reliability techniques, their expense, and the varying degrees of reliability required for different situations, most projects develop a reliability program plan to specify the reliability tasks that will be performed for that specific system.

The function of reliability engineering is to develop the reliability requirements for the product, establish an adequate reliability program, and perform appropriate analyses and tasks to ensure the product will meet its requirements. These tasks are managed by a reliability engineer, who usually holds an accredited engineering degree and has additional reliability-specific education and training. Reliability engineering is closely associated with maintainability engineering and logistics engineering. Many problems from other fields, such as security engineering, can also be approached using reliability engineering techniques. This article provides an overview of some of the most common reliability engineering tasks. Please see the references for a more comprehensive treatment.

Many types of engineering employ reliability engineers and use the tools and methodology of reliability engineering. For example:

System engineers design complex systems having a specified reliability
Mechanical engineers may have to design a machine or system with a specified reliability
Automotive engineers have reliability requirements for the automobiles (and components) which they design
Electronics engineers must design and test their products for reliability requirements.
In software engineering and systems engineering the reliability engineering is the subdiscipline of ensuring that a system (or a device in general) will perform its intended function(s) when operated in a specified manner for a specified length of time. Reliability engineering is performed throughout the entire life cycle of a system, including development, test, production and operation.

Reliability theory

Main articles: reliability theory, failure rate.

Reliability theory is the foundation of reliability engineering. For engineering purposes, reliability is defined as:

the probability that a device will perform its intended function during a specified period of time under stated conditions.

Mathematically, this may be expressed as,

$R(t)=\int_{0}^{t} f(x)\, dx \ \!$ ,

where $f(x) \!$ is the failure probability density function and

t

is the length of the period (which is assumed to start from time zero).

Reliability engineering is concerned with four key elements of this definition:

First, reliability is a probability. This means that failure is regarded as a random phenomenon: it is a recurring event, and we do not express any information on individual failures, the causes of failures, or relationships between failures, except that the likelihood for failures to occur varies over time according to the given probability function. Reliability engineering is concerned with meeting the specified probability of success, at a specified statistical confidence level.
Second, reliability is predicated on "intended function:" Generally, this is taken to mean operation without failure. However, even if no individual part of the system fails, but the system as a whole does not do what was intended, then it is still charged against the system reliability. The system requirements specification is the criterion against which reliability is measured.
Third, reliability applies to a specified period of time. In practical terms, this means that a system has a specified chance that it will operate without failure before time $t \!$ . Reliability engineering ensures that components and materials will meet the requirements during the specified time. Units other than time may sometimes be used. The automotive industry might specify reliability in terms of miles, the military might specify reliability of a gun for a certain number of rounds fired. A piece of mechanical equipment may have a reliability rating value in terms of cycles of use.
Fourth, reliability is restricted to operation under stated conditions. This constraint is necessary because it is impossible to design a system for unlimited conditions. A Mars Rover will have different specified conditions than the family car. The operating environment must be addressed during design and testing.

Toilet Install

Automatic or Drop-In Toilet Cleaners: Automatic or Drop-In Toilet cleaners usually consist of a disc of cleaner that you deposit into the toilet tank. Some other models suspend from the toilet tank or rim of the toilet. They automatically dispense cleaning solution into the water when the toilet is flushed.

Pros

An automatic cleaner is easy to use and easy to maintain.

Cons

The toilet will still need to be scrubbed occasionally. These cleaners aren't a good idea if you have pets or children who are likely to have access.

Powder Toilet Cleaners: Powder Toilet cleaners are designed to scrub a toilet without scratching it. These cleaners are a good choice when staining of the toilet bowl is an issue.

Pros

If you have rust or water deposit stains in your toilet bowl, using a powder cleanser offers enough scrubbing power without scratching your toilet.

Cons

Be careful not to scratch the surfaces of the toilet, which will allow future staining to occur more easily. Abrasive cleaners also require the use of an additional brush.

Toilet Brushes: Toilet brushes are bristle brushes that usually come with a storage container. Many companies market the toilet brushes to match bathroom decor.

Pros

A good toilet brush with stiff all-plastic brush and bristles does a great job at scrubbing a toilet. Don't choose a brush with bristles attached to wire. This can damage toilets.

Cons

A toilet brush needs to be thoroughly disinfected and/or kept away from areas where it could cross contaminate with bacteria. Cheap brushes can also damage the toilet.

Eye and Hand Protection:

Pros

Even the most experienced toilet cleaner can occasionally splash water and or cleaner during a good scrubbing. Protect your eyes with goggles and your hands with gloves. This is one of the filthiest places in your home. You do not want the contents or the cleaner anywhere near your eyes and hands.

Disposable Toilet Cleaning Systems: Almost every cleaning product company has some form of a disposable toilet cleaning system on the market. This systems allow you to have disposable prefilled cleaning heads, or automatic cleanser triggers that keep you from relying on a reusable brush and separate cleanser.

Pros

These systems save time because there is little cleanup. The cleaning systems work fairly well, although toilets with staining may still need a brush.

Cons

Disposable cleaners and cloths aren't friends to the environment.

Paper Towels vs. Rags: Sometimes it seems as though the outside has become dirtier than the bowl. Using paper towels, rags, or sponges along with a spray cleaner will get the outside as gleaming as the bowl.

Pros

Paper towels are able to be thrown away. There is no risk of contaminating other surfaces or laundry.

Cons

Paper towels aren't the most environmentally friendly choice for cleaning. Use rags if you prefer, but wash right away in hot water. Otherwise, go with paper towels, and never use sponges.