Iowa Admin. Code r. 875-140.3
In instances where the posting of a sign for each hazardous chemical would be ambiguous, repetitive, or where space is limited by the physical characteristics of the structure, or in situations, such as in a building, structure, or location, where a wide variety of materials may be stored having varying degrees of hazards, the identifying symbol shall indicate the most severe degree of hazard in each category except when a high hazard rating would be misleading because of the presence of an insignificant quantity of the material requiring the rating.
The employer and the local fire department may enter into a written agreement providing for the posting of signs for the most hazardous chemical in each principal category as set forth in subrule 140.1(2). The agreement is subject to the approval of the division pursuant to the procedure for a variance, as specified in rule 875-140.2 (89B). If the variance is approved, the employer shall post in the same location as the required posted signs a sign stating: "Signs not posted for all hazardous chemicals." The sign shall be in block letters at least 3 inches in height.
Iowa Admin. Code r. 875-140.3