ABSTRACT
Pe r s o n n e l involved in permit-required confined space entry must understand that some vapors or gases are heavier than air and will settle to the bottom o f a confined space. Other gases are lighter than air and will be found around the top o f the confined space. Because o f the behaviors o f various toxic gases, you must test all areas (top, middle, bottom) o f a con fined space with properly calibrated testing instruments to determine what gases are present (see Figure 10 .1 ).
