An excellent example of the application of Daltons law of partial pressures is the use of a liquid barometer to indicate atmospheric pressure. The barometer level indicates the sum of the partial pressure of water vapor and the partial pressure of the air. Partial pressures of air and water vapor are of great importance in psychrometry and are used to calculate the degree of saturation of the air or relative humidity at a specific dry-bulb temperature. 13.2.11 Relative Humidity and Specific Humidity Relative humidity is sometimes defined by the use of mole fractions, a difficult definition for psychrometric use. Hence, a more usable definition is desired. For this purpose, relative humidity may be closely determined by the ratio of the partial pressure of the water vapor in the air to the saturation pressure of water vapor at the same temperature, usually expressed as a percentage. Thus, dry air is indicated as 0% relative humidity and fully saturated air is termed 100% relative humidity. Computation of relative humidity by use of humidity ratios is also often done, but with somewhat less accuracy. Humidity ratio, or specific humidity Wa, at a specific temperature is the weight, lb, of water vapor in air per pound of dry air. If Ws represents the humidity ratio of saturated air at the same temperature (Table 13.2), then relative humidity can be calculated approximately from the equation W RH  a  100 (13.13)

fc
(15.29) D2 where D
distance, ft, from work plane to light source cp
candlepower of light source For a work plane at an angle  to the direction of the light source,  fc
cp sin (15.30) D2 In the metric system, illuminance is measured in lux, or lm/m2; 1 fc
10.764 lux. A luminaire is a lighting device that consists of one or more lamps, or light sources, a fixture that positions and shields them, components that distribute the FIGURE 15.11 Candlepower distribution curve indicates variation in lighting intensity with direction from a light source. light, and elements that connect the lamps to the power supply. In general, luminaires do not radiate light of equal intensity in all directions, because of the characteristics of the lamps or the geometry of the fixtures. The actual illuminance around a single luminaire is an important design consideration. This environment may be characterized by the candlepower distribution curve of the luminaire. A typical such curve for a light source symmetrical about two vertical, perpendicular planes is shown in

engineers liability insurance Damage to persons and property Amount of coverage Errors and omissions insurance Errors or omissions from the plans Highest available Amount of coverage Owner insurances Owners protective liability insurance Public liability and property damage as a result of construction operations Property fire insurance When construction is being done on an existing building, fire, etc., general contractor and subcontractors Full insurance value TABLE 17.1 Typical Insurance Needs of Parties to Construction (Continued) Type Purpose Suggested limits for small-to-mediumsize company Basis for premium Owner insurances Loss of use insurance Losses in property as result of fire or other loss Approx. Loss of income Steam boiler Explosion, etc. $500,000 Nuclear incident Nuclear reactor loss (if required) High * B.I.
bodily injury P.D.
property damage HMO
Health Maintenance Organization 1. Extended coverage endorsement, which insures the property for the same amount as the basic fire policy against loss or damage caused by windstorm, hail, explosion, riot, civil commotion, aircraft, vehicles, and smoke. 2. Vandalism and malicious mischief endorsement, which extends the protection of the policy to include loss caused by vandalism or malicious mischief. There is a special extended coverage form that provides coverage on an all-risk basis and includes the peril of collapse. Completed-value and reporting forms treat foundations of a building in the course of construction as a part of the Builders Risk Value for insurance purposes. But all work below the lowest basement slab, site work, and demolition are not covered by Builders Risk Insurance. The value of these items should be deducted from the amount of the policy. This will result in a saving of insurance premium. Builders machinery and equipment should be specifically insured as a separate item if coverage is desired under the policy. Under the terms of the AIA General Conditions, the owner is to provide the Builders Risk Insurance and pay for it. Under those circumstances, the contractor should request that the following clause appear as an endorsement to the policy: Additional insureds under this policy: The Contractor and its Subcontractors, as their interests may lie. This endorsement will assure the contractor and its subcontractors of a share in the insurance proceeds in case of claim. It further protects the contractor and subcontractors from suit by the insurance company under its subrogation clause, should either of these parties have caused or contributed to the loss. 17.15.2 Insurance for Contractors Equipment The so-called Inland Marine insurance market is the place to look for many coverages needed by contractors. From the insurance point of view, each contractors problem is considered separately. The type of operation, the nature of equipment, the area in which the contractor works, and other pertinent factors are all points considered by an Inland Marine underwriter in arriving at a final form and rate. Obvious contractors equipmentmechanical shovels, hoists, bulldozers, ditchers, and all other mobile equipment not designed for highway useis the primary subject of the Contractors Equipment Floater. Such protection is necessary because of the size of the investment in such equipment and of the multiplicity of perils to which the equipment is exposed. Some companies will write the Contractors Equipment Floater Policy only on a named-perils basis, which ordinarily includes fire, collision, or overturning of a transporting conveyance, and sometimes theft of an entire piece of equipment. Other companies will write certain kinds of contractors equipment on the so-called allrisk basis. Certain perils, such as collision during use, are subject to a deductible fixed amount. The rate for this broader insurance generally is higher than that for the named perils form. In the all-risk form, the customary exclusions, such as wear and tear, the electrical exemption clause, strikes, riots, and other similar exclusions, are present. Because of increased exposure to nuclear hazards, all Inland Marine policies that insure against fire must carry a nuclear exclusion clause that provides that the company shall not be liable for loss by nuclear reaction or radiation or radioactive contamination, whether controlled or uncontrolled and whether such loss is direct or indirect, approximate or remote. In addition to the equipment, there is a need to provide protection for the materials and supplies en route to or from the site. If these materials and supplies are transported at the risk of a contractor and are in the custody of a common carrier, a Transportation Floater should be obtained. If, on the other hand, these materials and supplies are moved on the contractors own trucks, a Motor Truck Cargo- Owners Form should be obtained. The premium for the transportation form is usually based on the value of shipments coming under the protection of the policy. The coverage is usually on an all-risk basis. The Motor Truck Cargo-Owners Form is generally on a named-perils basis at a flat rate applied against the limit of liability required by the insureds needs. Occasionally, a contractor may be responsible for machinery, tanks, and other property of that nature until such times as they are completely installed, tested, and accepted. Exposures of this kind are usually covered under an Installation Floater, which would provide insurance to the site as well. The Installation Floater Form is generally on a named-perils basis, including perils of loading and unloading, at a rate for the exposure deemed adequate by the underwriter. Large contractors should have such insurance written on a monthly reporting form to reflect increasing values as installation progresses. Small contractors generally can provide for the coverage under a stated amount on an annual basis subject to coinsurance. There is also a form of policy known as a Riggers Floater that is designed for contractors doing that type of work. This policy is usually a named-perils form at rates based on the nature of the rigging operation. Neither the forms nor rates in any of these classes are standard among the companies writing them, although in general they are all similar. Some contractors building bridges might be required to take a Bridge Builders Risk Form. This is an exception to most of the insurance provided to contractors, in that it is required to be rated in accordance with forms and rates filed in most of the states and administered by a licensed rating bureau. 17.15.3 Motor-Vehicle Insurance Loss and damage caused by or to motor vehicles should be separately insured under specific policies designed to cover hazards resulting from the existence and operation of such vehicles. Bodily injury or property damage sustained by the public as a result of the operation of contractors motor vehicles or other self-propelled equipment is insured under a standard policy of insurance. To secure complete protection, a Comprehensive Automobile policy should be obtained to provide protection, in addition to the preceding, for hired cars, employers nonownership, and any newly acquired motor vehicles or self-propelled equipment during the term of the policy. Damage to owned vehicles can be added to the same policy on an automatic basis to provide Comprehensive Coverage and Collision Insurance. All vehicles should be covered, for high limits. Protection furnished by automobile liability and property damage insurance serves in two ways: (1) the insurance company agrees to pay any sum for bodily injury and property damage for which the insured is legally liable, (2) the policy agrees to defend the insured. It is important, therefore, that the limits be adequate to guarantee that the insured obtain full advantage of the service available. For example, suppose only $25,000 and $50,000 limits are carried, and action is brought against the contractor in the amount of $500,000. It may be necessary to employ an attorney to safeguard the insureds interests for the amount of the action that exceeds the limits of the policy. A contractor should not operate any type of motor vehicle without insurance. Automatic coverage should be provided to include all motor vehicles owned or acquired. The cost for highest available limits is reasonable. Damage to owned motor vehicles may be insured under a fire, theft, and collision policy. Comprehensive motor-vehicle protection covers physical damage sustained by motor vehicles because of fires, theft, and other perils, including glass breakage. Collision insurance insures against loss from collision or upset. While the latter is available on a full-coverage basis, it is generally written on a deductible basis (loss