Those who do not live in seismically active zones should take these accounts to heart, as well. Other natural disasters and chemical explosions themselves can set off shock waves that empty chemical shelves and result in inadvertent mixing of chemicals. The NFPA fire hazard ratings, flash points, boiling points, ignition temperatures, and flammability limits of a number of common laboratory chemicals are given in Table 4.4 and in the LCSSs (see accompanying CD). The data illustrate the range of flammability for liquids commonly used in laboratories.
Over time, some chemicals continue to build peroxides to potentially dangerous levels, whereas others accumulate a relatively low equilibrium concentration of peroxide, which becomes dangerous only after being concentrated by evaporation or distillation. (See Chapter 6, section 6.G.3.) The peroxide becomes concentrated because it is less volatile than the parent chemical.
In some MSDSs, this list of toxic effects is quite lengthy and includes every possible harmful effect the substance has under the conditions of every conceivable use. Here, we aimed to investigate genes repressed by V. cholerae during intestinal colonization using an advanced version of the recombination-based expression technology. Having identified 101 in vivo repressed genes, initial characterization of a subset revealed that, in the majority of cases, in vivo silencing is essential to achieve full colonization fitness.
3.1. Cobalt II sulfate, CoSO4.7H2O
The possibility of serious injury or death by electrocution is very real if careful attention is not paid to engineering, maintenance, and personal work practices. Equipment malfunctions can lead to electrical fires. If there is a need to build, repair, or modify electrical equipment, the work should ideally be performed or, at a minimum, inspected by a trained and licensed electrician or electrical expert.
Teaching laboratories may introduce low-risk infectious agents as part of a course of study in microbiology. Nanoparticles have significantly greater relative surface areas than larger particles of an equivalent mass, and animal studies have demonstrated a correlation between biological effects (toxic response) and surface area. Thus, nanoparticles represent a greater toxic hazard than an equivalent mass of the same material in larger form.
Initial monitoring should be performed and repeated any time that there is a change in the use of formalin, which may result in an increase in exposure. Risk Management Issues All fresh specimens should be handled carefully, since each specimen represents a potential source of infectious material. Standard safety precautions, including the use of personal protective equipment, the use of a biological safety cabinet when working with infectious materials, and proper handling of chemicals, should be followed (7, 53-56). Material safety data sheets (MSDS) should be reviewed for all reagents used in the laboratory.
A related class of compounds includes inhibitor-free monomers prone to free radical polymerization that on exposure to air can form peroxides or other free radical sources capable of initiating violent polymerization. Note that care must be taken when storing and using these monomers-most of the inhibitors used to stabilize these compounds require the presence of oxygen to function properly, as described below. Always refer to the MSDS and supplier instructions for proper use and storage of polymerizable monomers.
Section 4.C discusses the toxic effects of laboratory chemicals by first presenting the basic principles that form the foundation for evaluating hazards for toxic substances. The remainder of this section describes how trained laboratory personnel can use this understanding and the sources of information to assess the risks associated with potential hazards of chemical substances and then to select the appropriate level of laboratory practice as discussed in Chapter 4.